ISSN:
1573-1421
Keywords:
Gold
;
hematite surface
;
surface complexation
;
adsorption
;
potentiometric titration
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Geosciences
Notes:
Abstract The acid/base properties of the hematite/water interface and surfacecomplexation with gold has been studied by potentiometric titrations in thefour component system H+ – ≡FeOH –AuCl 4 - – Cl-. Equilibrium measurementswere performed in NaCl media at 298.2 K. In the evaluation of equilibriummodel from experimental data the constant capacitance model was applied. Theacid/base properties were investigated in 0.1 M NaCl in the range 2.6 ≤pH ≤ 7.4. The resulting intrinsic constants for protonation anddeprotonation of hydroxyl groups at the surface were logβ 1,1,0,0(int) s = 7.10 ± 0.06 andlog β -1,1,0,0(int) s = - 7.80 ±0.06. The density of proton active surface sites was 2.85nm-2 and the specific capacitance 2.5 C V-1 m-2. In the investigation of surface complexation of gold, thepotentiometric titrations were performed in the range 2.0 ≤ pH ≤ 10.2.Titration data was supplemented with analysis of Au in the aqueous phase byatomic absorbance spectrometry. The equilibrium model proposed consists ofthe following monodentate surface complexes: ≡FeOHAuCl3(log β 0,1,1,-1 s = 1.45 ± 0.03),≡FeOHAuCl2OH (logβ -1,1,1,-2 s = -3.89 ± 0.02), ≡FeOHAu(OH)3 (logβ -3,1,1,-4 s = -21.94 ± 0.05). Aslightly better fit could be obtained by assuming formation of a bidentatecomplex with the composition(≡FeO)2Au(OH)H2O. However, based onstructural arguments this complex was rejected.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1009622915376
