『Abstract
The hydrolysis of iron (III) was studied in acid aqueous solutions
between 25 and 200℃ at saturated water vapour pressure by uv-vis
spectrophotometry using a high-temperature, flow-through gold-lined
optical cell. The strong ligand-to-metal charge transitions of
iron (III) hydroxo complexes at wavelengths below 400 nm were
used to obtain molar absorptivities, ε, and equilibrium hydrolysis
constants using principal component analysis of the spectra. The
total iron (III) concentrations ranged from 6.184×10-5
to 1.652×10-4 mol kg-1 and the perchloric
acid concentration was between 9.31×10-4 and 0.398
mol kg-1. Under these conditions two iron (III) species
identified, Fe3+ and FeOH2+, and the corresponding
hydrolysis constant according to the reaction
Fe3+ + H2O =FeOH2+
+ H+
increased from logβ1 = -2.18±0.01 at 25℃
to 0.54±0.15 at 200℃. The hydrolysis of Fe3+ to form
FeOH2+ is predominantly driven by positive entropy
indicating electrostatic interaction between Fe3+ and
OH-.
Keywords: Iron; Hydrolysis; Hydrothermal; Complexation; Spectrophotometry』
1. Introduction
2. Experimental methods
3. Results and discussion
3.1. Data treatment and spectral interpretation
3.2. Iron (III) hydrolysis in aqueous acid solutions
3.3. Previous results on iron (III) hydrolysis in hydrothermal
solutions
4. Conclusions
Acknowledgments
References