Complexation of Gold(III)-Chloride at the Surface of Hematite |
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| Authors: | Olga N Karasyova Lyudmila I Ivanova Leonid Z Lakshtanov Lars Lövgren Staffan Sjöberg |
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| Institution: | (1) Institute of Experimental Mineralogy, Russian Academy of Sciences, 142432 Chernogolovka, Moscow district, Russia;(2) Department of Inorganic Chemistry, University of Umeå, S-901 87 Umeå, Sweden |
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| 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 log
1,1,0,0(int)
s
= 7.10 ± 0.06 andlog
-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
0,1,1,-1
s
= 1.45 ± 0.03),FeOHAuCl2OH (log
-1,1,1,-2
s
= -3.89 ± 0.02), FeOHAu(OH)3 (log
-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. |
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| Keywords: | Gold hematite surface surface complexation adsorption potentiometric titration |
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