An EPR Investigation of Binding Environments by N-Donor Chelating Exchange Resins for Cu Extraction from Aqueous Media

Abstract

Chelating exchange resins (CERs) are now widely used for metal extraction in aqueous acidic media. Many of these CERs contain surface N-donor ligands, such as di(2-picolylamine) (BPA) and picolylamine (PA), which are highly selective for Cu(II) uptake. Two such widely used resins are Dowex M4195 and CuWRAM. Surprisingly, very little is known about the Cu(II) binding environments on the exchange resins, particularly at variable concentrations and pH's, and therefore we used EPR spectroscopy to investigate this binding. The broad EPR spectra of the Cu(II) loaded resins are quite complex, indicating the presence of multiple Cu(II) binding environments. By preparing a series of well-defined [Cu II (PA) x ] and [Cu II (BPA) x ] complexes and studying their EPR and UV−vis spectra, the individual Cu(II) species contributing to the broad and overlapping EPR spectra of the loaded resins were identified. For Dowex M4195, [Cu II (BPA)](H 2 O) m and [Cu II (BPA) 2 ] complexes are most dominant, whereas for CuWRAM two dominant species including [Cu II (PA) 2 ](H 2 O) m and [Cu II (PA) 3 ] were identified. Notably, [Cu II (PA)](H 2 O) m was not present in this sample. The experimental spin Hamiltonian parameters for all these species were in good agreement with the density functional theory derived values. Additional intermolecular Cu(II) species were identified on both resins, labeled [Cu II (BPA) x (BPA) y (H 2 O) n ] and [Cu II (PA) x (PA) y (H 2 O) n ]. The presence of coordinated water in these intermolecular anchored sites was confirmed in a series of dehydration−rehydration experiments. Furthermore, a series of acid elution experiments also confirmed that these species are less strongly coordinated to the resins compared to the intramolecular species [Cu II (BPA)](H 2 O) m , [Cu II (BPA) 2 ], [Cu II (PA) 2 ](H 2 O) m , and [Cu II (PA) 3 ]. Finally, while equilibrium batch uptake measurements revealed that the CuWRAM material had a much lower Cu(II) capacity compared to the polymeric Dowex material, the adsorbed copper can be recovered more efficiently using acid elution.

Laser-induced breakdown spectroscopy analysis of copper and nickel in chelating resins for metal recovery in wastewater

“…These resins display a wide range of selectivity values towards transition metals, which depend on the different stabilities of metal complexes at the required pH conditions 2 . Typically, chelating exchange resins facilitate increased adsorption rates, efficiencies, and surface areas when compared to ion exchange resins 24 , thus, chelating resin treatment is one of the most effective and attractive methods due to the simplicity of design and ease of operation 25 .…”

Split regeneration of chelating resins for the selective recovery of nickel and copper

“…The authors concluded that 90% of the nickel was stripped from the resin with 2 bed volumes of 20 g L -1 H 2 SO 4 while only 35% copper was stripped, suggesting that a split elution could be carried out to selectively recover both metals. Spencer et al [18] evaluated the complexation mechanisms and elution of copper using the resin Dowex M4195 and free ligands 2-picolylamine. Regarding copper desorption, the authors concluded that typically, the adsorbed copper ions are released by washing with concentrated acid (1.0 −2.0 M H 2 SO 4 ) which protonate the nitrogen sites.…”

Effect of the Diamagnetic Single-Crystalline Host on the Angular-Resolved Electron Nuclear Double Resonance Experiments: Case of Paramagnetic [nBu4N]2[Cu(opba)] Embedded in Diamagnetic [nBu4N]2[Ni(opba)]

“…In many instances, it provides great insights into structural and electronic arrangements otherwise unapproachable in research ranging from fundamental solid-state physics to medicine and biophysics. − Moreover, these studies are very important for the assessment of magnetic exchange interactions in the respective polynuclear and even in one-dimensional (1D), 2D, or 3D magnetic networks where the mononuclear TM complexes are used as building blocks. − In practice, from the analysis of ESR and ENDOR spectra, the tensors of the hyperfine (HF) and quadrupole (Q) interactions can be determined and, using specific models, the spin density distribution can be inferred. − An essential prerequisite for that is a well-resolved HF and Q structure of the spectra, which is rarely observed in concentrated solids due do the broadening effect of the dipole–dipole interaction. To eliminate this effect, paramagnetic complexes can be diluted in a nonmagnetic medium, in the simplest case in a suitable solvent.…”