Synergistic effect of 3,5-dichlorophenol and trioctylphosphine oxide on the extraction of vanadium(V) with 2-methyl-8-quinolinol derivatives.

The extraction of vanadium(V) with 2-methyl-8-quinolinol derivatives (HA), such as 2-methyl-8-quinolinol (HMQ), 2-methyl-5-butyloxymethyl-8-quinolinol (HMO4Q), and 2-methyl-5-hexyloxymethyl-8-quinolinol (HMO6Q), from a weakly acidic solution into chloroform was studied in both the absence and presence of 3,5-dichlorophenol (Hdcp) and trioctylphosphine oxide (TOPO) as the synergists. Vanadium(V) was extracted with HA as VO(OH)(A)2 in the absence of synergists, and its extractability increased with an increase in the hydrophobicity of HA. Vanadium(V) was quantitatively extracted from the lower pH region upon the addition of Hdcp and TOPO as VO(OH)(A)2 x Hdcp and VO2(A)(TOPO), respectively. The enhancement of the synergistic effect of Hdcp on the extraction of vanadium(V) with HA increased in the following order: HMQ < HMO4Q < HMO6Q, as opposed to that of TOPO. This result was ascribable to the difference in the mechanisms of the occurrence of the synergistic effect by Hdcp and TOPO.