Synergism of thiocyanate ions and microinterfacial surface as driving forces for heavy multi-metals extraction

A perspective of microemulsions in critical metal separation and recovery: Implications for potential application of CO2-responsive microemulsions

Since the discovery of microemulsions, they have attracted great attention due to its unique properties, such as ultra-low interfacial tension and nanoscale droplets. During the past several decades, microemulsions have shown unparalleled advantages in critical metal separation and recovery, e.g., high separation rate, high recovery efficiency, and good selectivity. Therefore, fundamental understandings of such metal recovery behavior are of great significance for the continuous development of microemulsion-based separation technology in this field. Herein, we first systematically reviewed the application of regular microemulsion in the separation and recovery process of critical metals focusing on their separation mechanisms. Then, we summarized the recent progress of CO2-responsive microemulsions and highlighted their potential application in critical metal separation and recovery, aiming to provide some insights into alleviating the difficulties in demulsification during the stripping stage using regular microemulsions. In this section, the latest development of CO2-responsive microemulsions is introduced, and the relationship between their composition, microstructure and macroscopic properties is discussed. Discussion and future perspectives are provided highlighting the design of new microemulsions and potential application of CO2-responsive microemulsions for metal separation and recovery in the future.

A new method for extraction and pre-concentration of the heavy metals using a microemulsion system in winsor II equilibrium and determination by HR-CS AAS

For the very first time, a microemulsion system in the Winsor II (WII) equilibrium was applied in a sample preparation method for extraction and pre-concentration in the determination of Pb, Cd, Co, Tl, Cu and Ni, in natural waters by high resolution continuum source atomic absorption spectrometry (HR-CS AAS). The method was optimized using the graphite furnace atomization. A simplex-centroid design for determine optimum extraction condition (77.5% aqueous phase, 5% of the oil phase, and 17.5% cosurfactant/surfactant ratio - C/S = 4) was applied. The optimized time for the sample preparations was around 30 min. The analytical performance of the optimized method using HR-CS GF AAS showed that the detection limits were: 0.09, 0.01, 0.06, and 0.05 μg L-1 for determination of Pb, Cd, Tl, and Co, respectively and the enrichment factors were between 6 and 19, considered excellent for all analytes. The RSD values were lower than 5%, demonstrating the good precision of the proposed method. When the optimized method was applied using the HR-CS F AAS, the sensibility increased 9 to 12 times for Cu and Ni, respectively. The analytical method was successfully applied for the determination of analytes in Certified Reference Material and real samples for natural waters such as Brackish water (recovery between 107 and 112%), Saline water (recovery between 83 and 94%), Produced water from oil industry (recovery between 98 and 110%) and Fresh water (recovery 80 and 87% to Cu and Ni respectively). All the results confirming the accuracy of the analytical method proposed. The repeatability of the measurements has been better 5% (n = 3), for all elements.

Microemulsions of Nonionic Surfactant with Water and Various Homologous Esters: Preparation, Phase Transitions, Physical Property Measurements, and Application for Extraction of Tricyclic Antidepressant Drugs from Aqueous Media

Microemulsions are nanocolloidal systems composed of water, an oil, and a surfactant, sometimes with an additional co-surfactant, which have found a wide range of practical applications, including the extractive removal of contaminants from polluted water. In this study, microemulsion systems, including a nonionic surfactant (Brij 30), water, and esters selected from two homologous series of C1-C6 alkyl acetates and ethyl C1-C4 carboxylates, respectively, were prepared by the surfactant titration method. Phase transitions leading to the formation of Winsor II and Winsor IV microemulsions were observed and phase diagrams were constructed. The dependences of phase transitions on the salinity and pH and the addition of isopropanol as a co-surfactant were also investigated. Some physical properties, namely density, refractive index, electrical conductivity, dynamic viscosity, and particle size, were measured for a selection of Winsor IV microemulsions, providing further insight into some other phase transitions occurring in the monophasic domains of phase diagrams. Finally, Winsor II microemulsions were tested as extraction solvents for the removal of four tricyclic antidepressant drugs from aqueous media. Propyl acetate/Brij 30/H2O microemulsions provided the best extraction yields (>90%), the highest Nernst distribution coefficients (~40-88), and a large volumetric ratio of almost 3 between the recovered purified water and the resulting microemulsion extract. Increasing the ionic strength (salinity) or the pH of the aqueous antidepressant solutions led to an improvement in extraction efficiencies, approaching 100%. These results could be extrapolated to other classes of pharmaceutical contaminants and suggest ester- and nonionic surfactant-based microemulsions are a promising tool for environmental remediation.

Amino Acid Leaching of Critical Metals from Spent Lithium-Ion Batteries Followed by Selective Recovery of Cobalt Using Aqueous Biphasic System

To reduce the exploitation of mine resources and decrease the harm to the environment caused by urban electronic wastes, the recovery of critical metals in secondary resources is crucial. In this study, we have successfully developed an eco-friendly process to integrate the leaching and separation of cobalt (Co) from a spent lithium-ion battery (LIB) cathode using an amino acid-based aqueous biphasic system (ABS). We, for the first time, demonstrated a simple method for leaching a LIB cathode using only amino acids. In addition, we have investigated the leaching mechanism using the typical cathode active material lithium cobalt oxide (LiCoO₂). Then, the Co was selectively extracted by a biphasic system (amino acid-PPG400-H₂O). This novel process has an excellent prospect in the field of spent-battery recycling because of its eco-friendly and process-simplified advantages.

Complex Extraction of Metals in an Aqueous Two-Phase System Based on Poly(Ethylene Oxide) 1500 and Sodium Nitrate

This article presents an ecologically safe aqueous two-phase system based on poly(ethylene oxide) with a molecular weight of 1500, designed for complex extraction of Ni(II), Co(II), Fe(III), Mn(II), Zn(II), Cu(II), and Al(III) from nitrate solutions. A kinetic dependence has been investigated for a distribution ratio for the metals examined. The influence of pH-values, temperature, initial metal concentration, and nitric acid content have on the extraction of a wide range of metals in the heterogeneous poly(ethylene oxide) 1500-NaNO₃-H₂O system has been discovered. As a result, the complex extraction of metals (E_Me > 60%) was achieved in one step of extraction without introducing additional chemicals into the system.