Thermodynamic modeling of metal–ligand interactions in high ionic strength NaCl solutions: the Ni2+-oxalate system

Abstract

AbstractStability constants for the 1:1 and 1:2 complexes of Ni(II)+Oxalate have been determined using solvent extraction. Data collected in 0.3m to 5.0m NaCl aqueous solutions at 20.0±0.1°C yielded values of logβ101ranging from 3.71 to 3.98(±0.06) and of logβ102from 6.44 to 6.95(±0.06), which agree well with values from the literature. The data were analyzed by the Pitzer model with a value ofμ0/RT=-17.47 for the 1:1 complex calculated from the data and literature values. A single neutral-ion interaction parameter λNiOx-Cl=-0.179 was used to describe the ionic strength dependence of the 1:1 complex. For the 1:2 complex, a value forμ0/RT=-11.31 and the Pitzer parameters values,β0NiOx₂²⁻-Na⁺=-0.0644 andβ1NiOx₂²⁻-Na⁺=0.8545, were determined. These standard chemical potential values are based on a model for oxalate deprotonation reported earlier.