Extension of the classical equilibrium analysis based on precise structure analysis of clustering phenomena by metal complexes

Okamura, Hiroyuki   ; Ueda, Yuki   ; Motokawa, Ryuhei   ; Mu, J.*; Masters, A. J.*; Antonio, M. R.*

Under practical liquid-liquid extraction conditions with high solute concentrations, clusters of metal-extractant complexes can form in the organic phase. In these conditions, application of the slope analysis method for determining metal-extractant stoichiometry becomes difficult, and the deviations from ideal appear as non-linear responses and non-integer slopes. In this study, we developed novel extraction equilibrium analysis for practical liquid-liquid systems with consideration of the cluster formation and investigated the extension of the classical equilibrium analysis. Molecular dynamics (MD) simulation snapshots indicate the formation of aggregated clusters of 1 to 9 Zr(NO)(TBP) complexes in -octane, leading to the determination of composition and molar fraction of each cluster. Considering the extraction equilibrium of clusters composed of Zr(NO)(TBP) complexes, the extraction equilibrium constants K ( = 1-9) were calculated from the distribution ratio and the molar fraction for each cluster obtained by the MD analysis. The distribution curve calculated from the obtained K values agrees well with the experimental values. Therefore, MD simulation can accurately reproduce the experimental values in the clustering/aggregation liquid-liquid extraction system, which enabled us to extend the classical equilibrium analysis.