Microscopic Insights into Extraction Mechanism of Copper(II) in Ammoniacal Solutions Studied by X-ray Absorption Spectroscopy and Density Functional Theory Calculation

Abstract

A microscopic investigation on the extraction process of copper(II) in ammoniacal solutions has been performed by X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculation. The structural change of copper(II) species in ammoniacal solution has been derived from X-ray absorption near-edge spectroscopy (XANES) by principal component analysis and linear combination fitting. It was found that the coordination structure of the extracted copper complex in the organic phases is planar square and independent of the aqueous pH, whereas the geometries of copper(II) species in ammoniacal solutions changed from axially elongated octahedron to distorted planar square with increase of pH. The coordination geometry and structural parameters of copper(II) species were further obtained by extended X-ray absorption fine structure (EXAFS) fitting and DFT calculation with the B3LYP functional. These results reveal that the formation of tetracoordinated copper(II) ammine species can evidently inhibit the copper extraction reaction. Thus, the extraction mechanism of copper(II) in ammoniacal solutions has been elucidated in view of the microscopic structural aspects of copper species in both organic phase and ammoniacal solutions.

Copper extraction using protic ionic liquids: Evidence of the Hofmeister effect

“…1. The choice of this set of ionic liquids is motivated by the observation that Cu 2+ coordinates strongly with both carboxylate [41][42][43] and amine [44] ligands. Indeed, high levels of extraction to organic solvents are observed when carboxylate and amine ligands are used in tandem to produce mixed-ligand complexes [45].…”

High Flux Recovery of Copper(II) from Ammoniacal Solution with Stable Sandwich Supported Liquid Membrane

“…Thus, the main transport resistance could be derived from the diffusion process of the copper complexes through the receiving phase/membrane interface. Based on the previous results, two carrier molecules can coordinate with per Cu ion to form the copper complexes with a planar square configuration, thereby increasing the molecular volume and viscidity of transport matters, which can increase their transport resistance . In practice, increasing temperature is favorable to the Cu­(II) transport, because of the decrease of viscosity of the extracted copper complexes at the higher temperature.…”

“…At pH 8.3, the transport efficiency of Cu­(II), Ni­(II), and Zn­(II) in the receiving phase is 75%, 7.4%, and 3.9%, respectively. Because water and ammonia molecules coordinate more easily with both nickel and zinc extracts than copper extract in the organic phase, − the extracted copper complex is more liable to transport in the hydrophobic sandwich SLM, because of its greater hydrophobic nature. Thus, the Cu­(II) in the ammoniacal solutions can be selectively transported over nickel and zinc into sulfuric acid solutions.…”

A novel strategy achieving enrichment of metal values from and into ammoniacal solutions

“…As increasing aqueous pH, ammonia molecules can gradually replace the coordinated water molecules in the hydrated metal ions, thus changing their geometric configuration and increasing the stability. Our previous microscopic investigations can conclude that zinc species of tetrahedral configuration [20] and copper species of planar configuration [21] can evidently inhibit the extraction reactions. Meanwhile, at high pH range, the hydroxyl can predominantly coordinate with metal species to form the mixed hydroxyammine complexes and hydroxo complexes.…”