Light-induced reduction of rhodium(III) and palladium(II) on titanium dioxide dispersions and the selective photochemical separation and recovery of gold(III), platinum(IV), and rhodium(III) in chloride media

Borgarello, Enrico; Serpone, Nick; Emo, Gary; Harris, R.; Pelizzetti, Ezio; Minero, Claudio

doi:10.1021/ic00245a010

Cited by 108 publications

(38 citation statements)

References 2 publications

(3 reference statements)

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“…1) that the Ce 3d spectra are readily modified under the incident beam and that CeO, is transformed into Ce203 : enhancement of the v' line, decrease of the other v lines; these phenomena also occur for the u lines but are more difficult to see (except for u"' ), owing to the overlapping of the v"' and u, u' lines. The same trend-reduction of CeO, into Ce203 under the incident beam-was found with a physical mixture Ti0,(80)-Ce02 (20), but to a lesser extent (Fig. 2), since the v' line appeared much more slowly.…”

Section: Supportssupporting

confidence: 73%

“…The spectra were all recorded after approximately half an hour in the incident beam. After impregnation, the catalysts showed similar features to the corresponding supports: cerium in oxidation state 111, and Ce("') with a small amount of Ce"") for the Ti0,(80)-Ce0, (20) and Ti0,(20)-Ce0,(80) mixtures, respectively. Upon treatment under air, some of the Ce'"') in Pt/Ti0,(80)-Ce0, (20) was oxidized to Ce('"), while mainly Ce(") was obtained for Pt/Ti0,(20~e0,(80) catalysts.…”

Section: Supportsmentioning

confidence: 85%

“…The mean grain diameter was between 80 and 310 pm. BET surface areas were determined by krypton adsorption at 196 K. Calcination of freshly prepared supports under air for 1 h resulted in a decrease in the surface areas from 330 to 240 m2 g-' and from 187 to 150 m 2 g-' for supports of relative percentage (TiO,(8O)-Ce0, (20) and Ti0,(20)-Ce0,(80), respectively. The second method was a simple physical mixture of both TiO, (P25, Degussa, 50 mz g-') and CeO, (RhBne-Poulenc, 130 m2 g-' ), analysed without any further treatment.…”

Section: Experimental *Pportsmentioning

confidence: 99%

“…All the physical mixtures of Ti0,-CeO, and the sol-gel-prepared Ti0,(80)-Ce0, (20) supports were impregnated by adding dropwise to the support a chloroplatinic solution at the desired concentration (2 cm3 per gram of support), followed by thorough mixing. Another method of impregnation was used for the sol-gel-prepared Ti0,(20)-Ce0,(80) support, which was placed on a Goosch filter.…”

Section: Catalystsmentioning

confidence: 99%

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Characterization by XPS and XAS of supported Pt/TiO₂CeO₂ catalysts

Dauscher

Hilaire

Normand

et al. 1990

Surface & Interface Analysis

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Section: Supportssupporting

confidence: 73%

Section: Supportsmentioning

confidence: 85%

Section: Experimental *Pportsmentioning

confidence: 99%

Section: Catalystsmentioning

confidence: 99%

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Characterization by XPS and XAS of supported Pt/TiO₂CeO₂ catalysts

Dauscher

Hilaire

Normand

et al. 1990

Surface & Interface Analysis

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“…Some research groups (4)(5)(6)(7)(8) have shown the viability of the photochemical deposition and recovery of metallic gold from aqueous solutions of chloride species like AuCl 3 and AuCl 4 -in the presence of titania. These species are considered easy to reduce, due to their reduction potential of E 0 = +1.0 V NHE (NHE, normal hydrogen electrode), whereas the value of the reduction potential in oxygenated systems for Au(CN) 2 -is E 0 = -0.6 V NHE.…”

Section: Introductionmentioning

confidence: 99%

Photocatalytic gold recovery from spent cyanide plating bath solutions

et al. 2005

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Gold-cyanide compounds represent the gold-containing chemicals most widely used in mining and electroplating industries. Despite many efforts focused on the substitution of cyanide salts by less toxic compounds, no successful alternatives have been found. The unique complexing capabilities of cyanide ions in aqueous solutions make these compounds the best choice for the heap leaching process in the gold mining sites or for gold plating applications (1).Wastewater effluents of these processes show significant concentrations of gold-cyanide complexes (2) that, due to its high stability, are very difficult to remove using the conventional oxidation technologies for cyanide degradation (3). Recovery of the gold present in the spent plating bath solutions, a desirable process from an economical standpoint, is currently carried out mainly by electrolysis and ion exchange processes.Some research groups (4-8) have shown the viability of the photochemical deposition and recovery of metallic gold from aqueous solutions of chloride species like AuCl 3 and AuCl 4 -in the presence of titania. These species are considered easy to reduce, due to their reduction potential of E 0 = +1.0 V NHE (NHE, normal hydrogen electrode), whereas the value of the reduction potential in oxygenated systems for Au(CN) 2 -is E 0 = -0.6 V NHE. However, to the best of our knowledge, there are no references in the literature about the TiO 2 -assisted photocatalytic decomposition of gold-cyanide complexes. Serpone et al. (6) reported the only work in which gold was deposited from air-equilibrated solutions prepared by mixture of NaCN and AuCl 3 ·3H 2 O. No trials for characterization of the gold-cyanide complexes that could be formed in the system were done. The goal of their work was to investigate the disposal of free CN -by oxidation with peroxides prior to irradiation of the solutions in the presence of TiO 2 . The fast oxidation of free cyanides avoided the formation of gold-cyanide complexes thus allowing Au(III) reduction on irradiated TiO 2 .On the other hand, the photocatalytic processes have shown a high efficiency for the oxidation of free cyanides (9,10), iron cyanocomplexes (11,12) and copper cyanocomplexes (13).In this work, a new procedure for gold recovery from solutions containing gold-cyanide complexes by using TiO 2 -based semiconductor materials is reported. The photocatalytic treatment performed in the absence of oxygen leads to the reduction of gold to the metallic state and increases the availability of cyanide for subsequent oxidation treatment (14).

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