Distribution Analysis of Complexes Using the Optimization of Thermodynamic Model

Various chemical reactions are utilized in the metallurgical industry, such as electrorefining, ion-exchange, solvent extraction, and so on. Identifying the materials involved is essential for a proper understanding of chemical reactions. However, the distributions of metal complexes reported to date are unlikely to be accurate, and discrepancies have been observed between these distributions and their adsorption behaviors to ion exchangers. Hence, the optimization of thermodynamic models has been developed to obtain accurate chemical conditions of complexes. This method is based on the Lambert-Beer law and consists of the first derivative test to determine the number of complex species and optimizations of thermodynamic models to accurately reproduce a series of UV-Vis absorption spectra. The thermodynamic models to be optimized are built on complex formation reactions, mass balances, and electrical neutrality. Activity coefficients of charged and neutral species were estimated using the Debye-Hückel model and the Setchénow equation, respectively. The EQBRM code is employed to calculate concentrations of species. In addition, approaches for verifying the obtained results were investigated, such as ion exchange behaviors and complex structure analysis using X-ray absorption spectroscopy. In this manner, the thermodynamic model optimization method excludes subjectivity and preconceived notions, thereby enabling the derivation of a rational conclusion. This paper illustrates the procedure referring to the analysis of the distribution of cobalt chloro complexes in hydrochloric acid solutions as an example. “kbetar” is an analysis package developed in the R environment for reliable analysis.