A study of adsorption and absorption mechanisms of copper in palygorskite

Abstract

Desorption experiments performed on four Cu-adsorbed palygorskites suggest that the leached Cu2+ ion originates at the surface and/or net-like interstice of the palygorskite fibres. The leached fraction, calculated from the quantities of adsorbed Cu2+ before and after desorption, is <1%. This may indicate that the majority of Cu is in inaccessible structural sites. X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared (FTIR) spectroscopy and electron spin resonance (ESR) were used to determine the mineralogical character of the Cu-adsorbed palygorskite. Two photoelectron lines at 932.5 and/or 933.7 eV in the narrow scan Cu 2p3/2 spectra show that Cu adsorbed on the surface of palygorskite is in the Cu+ and Cu2+ state. The stretching vibrations of the octahedral cation shift ~3–5 cm–1 towards a greater wavenumber in the FTIR spectra of Cu-adsorbed palygorskite. It can be deduced that the Cu2+ is trapped in the channel of the palygorskite structure. The ESR spectra of the palygorskite give g values of 2.34, 2.12, 2.08 and 2.05, suggesting that some Cu ions cannot be reached by H+. These results confirm that Cu is adsorbed by palygorskite via three possible mechanisms: (1) the Cu is adsorbed onto the surface or in a net-like interstice, and its oxidation states are +1 and +2; (2) Cu forms a complex ion – [Cu(H2O)4]2+ or [Cu(H2O)6]2+, and is trapped in the channel; or (3) Cu enters into the hexagonal channel of the tetrahedral sites or the unoccupied octahedral sites of palygorskite.

Rapid degradation of atrazine by hydroxyl radical induced from montmorillonite templated subnano-sized zero-valent copper

“…2), the copper species in the original Cu 2+ -montmorillonite is Cu 2+ (935.5 eV) (Koppelman and Dillard, 1977). A strong peak corresponding to Cu + (933.2 eV) was also observed, which is consistent with the results of Cai and Xue (Cai and Xue, 2008), and can be explained by the photo-reduction process induced with the X-ray irradiation. After NaBH 4 reduction, most of copper turns into ZVC (932.2 eV), with a small shift compared to the standard binding energy of Cu 0 (932.4 eV) due to the small particle size effect (Oberli et al, 1981).…”

Removal of Cu(II) from aqueous solutions using dolomite–palygorskite clay: Performance and mechanisms

“…In general, many types of possible mechanisms are involved in the removal process of metal ions by these two groups of minerals, such as ion exchange, surface complexation, physical adsorption and surface precipitation (Cai and Xue, 2008;S.X. Chen et al, 2004;Chen et al, 2007;Pehlivan et al, 2009;Walker et al, 2004).…”

Development of innovative environmental applications of attapulgite clay

“…replacement of Mg 2+ in the edges of octahedral layer and inner-sphere complexation on the functional groups on the broken edges of the mineral. Furthermore data of Cai & Xue (2008) confirmed three mechanisms for copper adsorption by palygorskite: (a) onto the surface or in a net-like interstice; (b) forms a Me-complex ion and is trapped in the channel; or (c) into the hexagonal channel of the tetrahedral sites or the unoccupied octahedral sites of the mineral.…”