Chemical equilibrium studies on the nickel sulfate-acetate buffer/β-alkyl-8-hydroxy-quinoline-xylene system

Abstract

A thermodynamic equilibrium model is developed for the distribution of nickel between two phases for the system nickel sulfate-acetate buffer/β-alkyl-8-hydroxy quinoline in xylene. Chemical equilibrium data were obtained for the range of experimental parameters of [Ni]aq,i (0.00435 to 0.01740 mol/dm3), pH (3.90 to 4.95), extractant [HR]org,i (0.02 to 0.06 mol/dm3), and temperature (25 to 50°C). The best fit of the data results with the following equation: $$ \ln \frac{{[\overline {{\text{NiR}}} _2 ][{\text{H}}^{\text{ + }} ]^2 }} {{[{\text{Ni}}^{{\text{ + + }}} ][\overline {{\text{HR}}} ]^2 }} = - 12.73 - 4430\left( {\frac{1} {T} - \frac{1} {{308}}} \right) $$ The above analysis requires specification of the aqueous phase ionic concentrations which are analyzed by considering the pertinent species equilibria. Also, the stoichiometric coefficients of two for hydrogen ion and β-alkyl-8-hydroxy-quinoline are determined for the extraction reaction using aqueous phase modeling and a statistical fit of equilibrium data. The results indicate that the enthalpy of the reaction and the entropy change are 36.8 kJ/mol and 13.8 J/mol-K, respectively.