Properties of 4-(1´-n-tridecyl)pyridine N-oxide in the extraction and polymer inclusion membrane transport of Cr(VI)

The N-oxide of 4-(1´-n-tridecyl)pyridine (TDPNO) is a novel agent which could be used for the separation of Cr(VI) from aqueous solutions of sulphuric acid. The distribution constants (KD) of TDPNO in the systems: toluene/0.5M (Na,H)2SO4 and toluene-n-heptane (3:1) mixture/0.5M (Na,H)2SO4, were found to be 2350±30 and 2180±20, respectively. The protonation constant of TDPNO (KH=12.0±0.1) was also determined. The interfacial activity of TDPNO in the systems hydrocarbon/water was found to be strongly dependent upon the Lewis basicity of hydrocarbons. The chromium(VI) extraction and transport with TDPNO in the CTA-based polymer inclusion membrane system were found to be strongly dependent upon the concentration of sulphuric acid in the aqueous and/or source phase, respectively. The complex L·H2CrO4, where L stands for TDPNO, was found to occur in the organic phase and/or at the source phase/membrane phase boundary.