The Distribution and Structures of Ferric Aqua and Chloro Complexes in Hydrochloric Acid Solutions

Knowledge of the distribution of metal chloro complexes in hydrochloric acid solutions is fundamental for constructing an efficient hydrometallurgical process. The condition of chemical species in the aqueous phase is important for understanding adsorption reactions as well as the properties of functional groups. The distribution of ferric aqua and chloro complexes was determined by fitting thermodynamic models to a series of UV-vis absorption spectra. In addition, X-ray absorption spectra of individual species were obtained by decomposition of a series of raw spectra by the distribution of ferric aqua and chloro complexes, and each structure was determined. Analyses using the UV-vis and X-ray absorption spectra complement each other and offer more reliable results than the conventional methods. Five ferric aqua and chloro complexes of [FeIII(H2O)eq4(H2O)ax2]3+, [FeIIIClax2(H2O)eq4]+, [FeIIICleq3(H2O)ax2]0, [FeIIICl4]–, and [FeIIICleq4Clax2]3– were observed and the thermodynamic parameters of the formation reactions were successfully determined.