Three-Liquid-Phase Extraction Procedure.
Extraction experiments were performed in 50 mL graduated centrifugal
tubes by taking fixed volumes of organic (5 mL) and aqueous (20 mL) phases.
In all experiments, 30% (v/v) D2EHPA in n-hexane was used as the organic phase, whereas a mixture
containing 4 g of PEG (8 mL of PEG stock solution) and 4 g of (NH4)2SO4 [8 mL of (NH4)2SO4 stock solution] was used as the aqueous phases, unless otherwise stated. After mixing of the organic
and aqueous phases and pre-equilibration for a while,1 mL of Cr stock 1 was added,except in the study of the initial chromium amount, for which Cr stock 2 was used.
The system was made to volume (25 mL) with deionized water.
Note that,except for the investigation of the effects of the aqueous pH, the pH of the (NH4)2SO4-rich bottom phase of the pre-equilibratedTable 1.
Extraction of Cr(III) and Cr(VI) as a Function of
pHini and pHeq in the Three-Liquid-Phase System