Extraction behavior of Ga(III) and Pd(II) with 2-methyl-8-quinolinol derivatives into supercritical fluid CO 2

Abstract

The extraction behavior of gallium(III) and palladium(II) with 2-methyl-8-quinolinol (HMQ), 2-methyl-5-hexyloxymethyl-8-quinolinol (HMO 6Q) and 5-hexyloxymethyl-8-quinolinol (HO 6Q) from an acidic solution into supercritical fluid (SF) CO 2 were investigated. Furthermore, the pH of an acidic solution contacting with SF CO 2 was spectrophotometrically measured, and the distribution constants of HMO 6Q between SF CO 2 and water were also determined at I = 0.1 M (H, Na)NO 3, 45°C, and 8.6 – 20.4 MPa. Above pH 3, the pH of the aqueous phase in contact with SF CO 2 was levelled to about 3. On the other hand, below pH 3, the pH change is negligibly small. The distribution constant ( K D,SF CO2 of HMO 6Q between SF CO 2 and water at 20.4 MPa was about one tenth of the K D for heptane - water system, indicating that the solubility of HMO 6Q in SF CO 2 is remarkably smaller compared with that in heptane. The Ga(III)-HMO 6Q and Ga(III)-HO 6Q complex extracted into SF CO 2 were assigned to be Ga(OH)(MO 6Q) 2 and Ga(O 6Q) 3, respectively. Palladium(II) was extracted with HMQ as Pd(MQ) 2 from a weakly acidic solution. Even in the presence of HMQ, the Pd(II)-HMQ complex extracted from the higher HCl concentration should be H 2PdCl 4.