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Observation of the adsorption of K+Au(CN)2- ion pairs on the surface of nanoporous carbon by XANES

Lookup NU author(s): Emeritus Professor Mark Thomas

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Abstract

The adsorption of dicyanoaurate(I) complexes on nanoporous carbon is widely used for the recovery of gold in the extractive metallurgy industry. However, there is no agreement on the adsorption mechanism concerning the nature of the adsorbed species on carbon surface. A novel experiment was designed in this study by treating the adsorbed dicyanoaurate(I) with 18-crown-6, which has a strong affinity for the K+ ion, followed by nitrogen K-edge XANES measurement, which is sensitive to the chemical environment of the absorbing atom. The results showed that there was a red shift of the lowest energy transition (K →π* resonance) of the nitrogen atom from 401.0 to 399.7 eV after the adsorbed dicyanoaurate(I) was treated with 18-crown-6 because of increased electron densities on N atoms, indicating that the K+ ions were coadsorbed with dicyanoaurate(I) complexes as K+Au(CN) 2- ion pairs. The nitrogen K →π* resonance energy of dicyanoaurate(I) decreased upon adsorption as K+Au(CN) 2- ion pairs compared with KAu(CN)2 solid (401.3 eV to 401.0 eV). This is probably due to decreased Au-Au association, which increases π-back-donation from metal centers to CN ligands thereby increasing electron densities on the nitrogen atoms accordingly. A minority of the dicyanoaurate(I) was adsorbed as unpaired Au(CN)2- ions species. The unpaired adsorption was partly suppressed by the presence of Ca2+ ions. The novelty of the approach used in this work is applicable to the research of other adsorption systems.


Publication metadata

Author(s): Jia Y, Thomas KM

Publication type: Article

Publication status: Published

Journal: Journal of Physical Chemistry B

Year: 2004

Volume: 108

Issue: 44

Pages: 17124-17128

ISSN (print): 1520-6106

ISSN (electronic): 1520-5207

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/jp0378900

DOI: 10.1021/jp0378900


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