Insight into the interaction between zirconium dibutyl phosphate complex and diluents: An experimental and computational study

Abstract

In solvent extraction processes, there are challenges caused by the formation of the third phase or interfacial precipitation. The branched alkanes have been used as diluents to disrupt the third-phase formation, while there is little study about the effect of diluents on the appearance of precipitation. Here, we report the inhibiting effect of the novel hyperbranched alkane diluent (HAD) on the formation of zirconium-dibutyl phosphate (Zr-DBP) precipitation and investigate the formation mechanism by the density functional theory (DFT) theory. The extraction experiments show that HAD as the diluent has a remarkable inhibiting ability to form Zr-DBP precipitation, compared with n-dodecane and kerosene. The spectra show no noticeable difference in the composition and structures of the precipitations formed in the three diluents. The energetics from the DFT calculations suggest the P-OH and P=O ligands on one HDBP molecule can bridge two Zr-DBP complexes into a dimer and then aggregate into the precipitation. Besides, the interactions between diluent-diluent molecules play a significant role in precipitation formation. The straight-chain n-dodecanes have a strong intermolecular dispersion force and tend to attract each other but not the Zr-DBP complex. However, the branched alkanes with weak intermolecular interactions have a better dispersive capacity for Zr-DBP complexes, due to the much higher dispersion force of diluent-complex interaction than that of the diluent-diluent interaction. This work provides a new insight into the formation of interfacial crud from the interactions between solutes and diluents of the organic phase in solvent extraction.