Determination of the Distribution of Ferric Chloro Complexes in Hydrochloric Acid Solutions at 298 K

Abstract Understanding the intrinsic nature of materials requires ultrahigh-purity materials because impurities affect various properties. Ion-exchange separation is one of the most promising purification technologies; however, the thermodynamic details of the ion-exchange reaction have not been made clear. The condition of metal species in the solution phase is fundamental to investigating the ion-exchange reaction. In this paper, the distribution of ferric chloro complexes in hydrochloric acid solutions was investigated by factor analysis of UV-Vis absorption spectra, followed by fitting analysis of a theoretical model to individual molar attenuation coefficients obtained by mathematical decomposition of UV-Vis absorption spectra. Five ferric species were detected by principal component analysis using a novel index proposed in this paper. In the results of factor analysis followed by fitting analysis, [FeIII]3+, [FeIIICl]2+, [FeIIICl2]+, [FeIIICl3]0, and [FeIIICl4]− were identified. The activity coefficients of charged species in concentrated aqueous solutions were estimated by using a modified Debye-Hückel equation. The thermodynamic parameters of the four cumulative formation constants and a Setchénow coefficient for neutral species of [FeIIICl3]0 were determined. The adsorbability of ferric, cupric, and cobalt species to an anion exchanger from hydrochloric acid solutions was qualitatively discussed using the results obtained in this paper.