M. Borkowski et al., Thermodynamic modeling of metal-ligand interactions in high ionic strengthNaCl solutions: the Co2+-citrate and Ni2+-citrate systems, INORG CHIM, 298(2), 2000, pp. 141-145
The complexation of Co(II) and Ni(II) by citrate in 0.3-5 m NaCl solutions
has been investigated. The stability constants for CoCit(-) and NiCit(-) we
re measured as a function of NaCl concentration using a solvent extraction
method with HDEHP in toluene. The stability constants for both complexes de
creased with increasing NaCl concentrations up to 5 m. The data were modele
d using the ion-interaction formalism developed by Pitzer. The dimensionles
s standard chemical potentials for the CoCit(-) and NiCit(-) complexes were
calculated to be - 2.561 and - 0.697, respectively. Binary interaction par
ameters calculated in this work were beta(0) = - 0.2249 and C-Phi = 0.0539
for NiCit(-) and Na+ interactions and beta(0) = - 0.5407 and C-Phi = 0.1353
for CoCit(-) and Na+ interactions. Because of limited data, the B-(1) valu
e for both CoCit(-) and NiCit(-) with Na+ was fixed at an average value of
0.29 which was obtained by averaging 1-1 interactions for other carboxylic
acid salts. Higher order interaction parameters wen not required to model t
he data. (C) 2000 Elsevier Science S.A. All rights reserved.