Studies on Gold Complexes. III. The Standard Electrode Potentials of Aqua Gold Ions.

Skibsted, Leif H.; Bjerrum, Jannik; Sandström, Joakim; Wennerbeck, Ingegerd; Williams, Mark A.; Andresen, Arne F.

doi:10.3891/acta.chem.scand.31a-0155

Cited by 30 publications

(16 citation statements)

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“…We tried an alternate approach by starting with [AuBr 4 ] À and adding iodide, but this was also unsuccessful. Although formation constants for the [AuI 4 ] À species have been reported by several authors (Latimer, 1952;Finklestein and Hancock, 1974;Skibsted and Bjerrum, 1977;Wagman et al, 1982), the only experimental study appears to be an electrochemical one where the complex may be observed as a short-lived reversible reaction product in cyclic voltammetry (Qi and Hiskey, 1993). Table 2 Halide and gold concentrations, pH and temperature used to measure UV-Vis absorbance spectra of mixed complexes of Au(III) with Cl À , Br À and OH À .…”

Section: Solution Preparationmentioning

confidence: 95%

A spectrophotometric study of aqueous Au(III) halide–hydroxide complexes at 25–80°C

Usher

McPhail

Brugger

2009

Geochimica et Cosmochimica Acta

184

155

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Section: Solution Preparationmentioning

confidence: 95%

A spectrophotometric study of aqueous Au(III) halide–hydroxide complexes at 25–80°C

Usher

McPhail

Brugger

2009

Geochimica et Cosmochimica Acta

184

155

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“…2). Given the great stability of the Au(S 2 O 3 ) 2 3À complex at ambient conditions (log 10 b (Au(S 2 O 3 ) 2 3À ) = 28.0, 2 Skibsted and Bjerrum, 1977), such thiosulfate concentrations are potentially sufficient to complex all dissolved gold in our experiments in acidic solutions. In situ Raman spectroscopy measurements of Bondarenko and Gorbaty (1997), carried out between 200 and 500°C at 1000 bar on pure water saturated with sulfur, revealed the growth with T of bands tentatively attributed to H n S 2 O 3 nÀ2 , S 8 or H 2 S n species.…”

Section: # Run Initial Composition a T (°C) Fluid Density C (G/cm 3 )mentioning

confidence: 98%

A new view on gold speciation in sulfur-bearing hydrothermal fluids from in situ X-ray absorption spectroscopy and quantum-chemical modeling

Pokrovski¹,

Тагиров²,

Schott³

et al. 2009

Geochimica et Cosmochimica Acta

125

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Despite the common belief that Au I complexes with hydrogen sulfide ligands (H 2 S/HS À ) are the major carriers of gold in natural hydrothermal fluids, their identity, structure and stability are still subjects of debate. Here we present the first in situ measurement, using X-ray absorption fine structure (XAFS) spectroscopy, of the stability and structure of aqueous Au I -S complexes at temperatures and pressures (T-P) typical of natural sulfur-rich ore-forming fluids. The solubility of native gold and the local atomic structure around the dissolved metal in S-NaOH-Na 2 SO 4 -H 2 SO 4 aqueous solutions were characterized at temperatures 200-450°C and pressures 300-600 bar using an X-ray cell that allows simultaneous measurement of the absolute concentration of the absorbing atom (Au) and its local atomic environment in the fluid phase. Structural and solubility data obtained from XAFS spectra, combined with quantum-chemical calculations of species geometries, show that gold bis(hydrogensulfide) Au(HS) 2 À is the dominant Au species in neutral-to-basic solutions (5.5 6 pH 6 8.5; H 2 O-S-NaOH) over a wide range of sulfur concentrations (0.2 < RS < 3.6 mol/kg), in agreement with previous solubility studies. Our results provide the first direct determination of this species structure, in which two sulfur atoms are in a linear geometry around Au I at an average distance of 2.29 ± 0.01 Å . At acidic conditions (1.5 6 pH 6 5.0; H 2 O-S-Na 2 SO 4 -H 2 SO 4 ), the Au atomic environment determined by XAFS is similar to that in neutral solutions. These findings, together with measured high Au solubilities, are inconsistent with the predominance of the gold hydrogensulfide Au(HS) 0 complex suggested by recent solubility studies. Our spectroscopic data and quantum-chemical calculations imply the formation of species composed of linear S-Au-S moieties, like the neutral [H 2 S-Au-SH] complex. This species may account for the elevated Au solubilities in acidic fluids and vapors with H 2 S concentrations higher than 0.1-0.2 mol/kg. However, because of the complex sulfur speciation in acidic solutions that involves sulfite, thiosulfate and polysulfide species, the formation of Au I complexes with these ligands (e.g., AuHS(SO 2 ) 0 , Au(HS 2 O 3 ) 2 À , Au(HS n ) 2 À ) cannot be ruled out. The existence of such species may significantly enhance Au transport by high T-P acidic ore-forming fluids and vapors, responsible for the formation of a major part of the gold resources on Earth.

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“…In recent years some studies have been carried out, in order to formulate electroforming baths with different Au complexes and electrolytes. At the present time, complexes based on sulfite, 1,2 thiosulfate 3-5 or amines 6 are considered promising alternatives, moreover they exhibit good stability constants, suitable redox potential 7,8 and good throwing power. 9 Nevertheless, the use of these complexes is not common in jewelry electroforming production because their syntheses are laborious and the baths need stabilizers and/or brightners that raise the electrolyte service life and promote suitable film growth.…”

mentioning

confidence: 99%

Electroformed objects for jewelry: secondary ion mass spectrometry characterization of Au films from CN-free electrolytes

Fabrizio

Piccirillo

Daolio

1998

Rapid Commun. Mass Spectrom.

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CN-free electrolytic baths were studied in order to deposit thick Au films on different cathodic substrates. Secondary ion mass spectrometry characterization of electrodeposited gold for jewelry is presented, analyzing surface composition and element distribution along the thickness. It was verified that additives used to improve the deposits are included in the coatings during the electrolysis. Cathodic substrates utilized for the electrodeposition were detected on the surface spectra, suggesting intermetallic diffusion along the deposits. #

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Studies on Gold Complexes. III. The Standard Electrode Potentials of Aqua Gold Ions.

Cited by 30 publications

References 0 publications

A spectrophotometric study of aqueous Au(III) halide–hydroxide complexes at 25–80°C

A spectrophotometric study of aqueous Au(III) halide–hydroxide complexes at 25–80°C

A new view on gold speciation in sulfur-bearing hydrothermal fluids from in situ X-ray absorption spectroscopy and quantum-chemical modeling

Electroformed objects for jewelry: secondary ion mass spectrometry characterization of Au films from CN-free electrolytes

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