Third Phase Formation in the Solvent Extraction System Ir(IV)—Cyanex 923

Abstract

The splitting of a system from biphasic to triphasic was studied in the liquid‐liquid extraction of Ir(IV) and HCl using Cyanex 923 (C923). The limiting organic concentrations (LOC) of Ir(IV), which are the maximum possible concentrations of Ir(IV) in the organic phase without the formation of a third phase, were determined under different experimental conditions. The experimental conditions investigated were: concentrations of HCl and NaCl in the aqueous phase, concentrations of C923 and a modifier (tributyl phosphate (TBP) or decanol) in the organic phase, and an organic phase made with different diluents such as n‐octane, n‐nonane, n‐dodecane, kerosene, cyclohexane, toluene, and xylene. The formation of a third phase depends on the concentration of Ir(IV) and HCl in the aqueous phase, as well as on the other experimental conditions. The third phase appeared without Ir(IV) when the concentration of HCl in the equilibrated aqueous phase was 3.5 M and the organic phase contained 10% (v/v) C923/kerosene. The maximum LOC of Ir(IV) was obtained when the initial concentration of HCl in the aqueous phase was 2 M. The LOC of Ir(IV) can be increased though the addition of typical solvent modifiers (such as TBP or decanol) in the organic phase. The LOC of Ir(IV) varied significantly when it was extracted from an aqueous solution containing different concentrations of NaCl. The values obtained for the LOC using different diluents were in the following decreasing order: toluene ≈ xylene>cyclohexane>n‐octane>n‐nonane>kerosene>n‐dodecane. No third phase was detected when toluene and xylene were used as diluents. In the case of cyclohexane, no third phase was observed when the aqueous phase contained 4 M HCl. Spectral studies were performed to investigate the chemical composition of the third phase obtained with Ir(IV)‐HCl‐C923.

Keywords:

• Triphasic formation
• HCl
• LOC

Acknowledgments

This work was financed by the European Commission (contract CRD‐CT‐2000‐00300) within the framework of the Growth Program and MCYT (contract PPQ2002‐04267). C. S. Kedari acknowledges the financial support of DURSI grant 2002PIV‐00065 (through the Generalitat of Catalonia).

Additional information

Notes on contributors

C. S. Kedari

on leave from Bhabha Atomic Research Centre, Trombay, Mumbai.