Extraction behavior of Ga(III) and Pd(II) with 2-methyl-8-quinolinol derivatives into supercritical fluid CO2

The extraction behavior of gallium(III) and palladium(II) with 2-methyl-8-q uinolinol (HMQ), 2-methyl-5-hexyloxymethyl-8-quinolinol (HMO(6)Q) and 5-hex yloxymethyl-8-quinolinol (HO(6)Q) from an acidic solution into supercritica l fluid (SF) CO2 were investigated. Furthermore, the pH of an acidic soluti on contacting with SF CO2 was spectrophotometrically measured, and the dist ribution constants of HMO(6)Q between SF CO2 and water were also determined at I = 0.1 M (H, Na)NO3 45 degreesC, and 8.6 - 20.4 MPa. Above pH 3, the p H of the aqueous phase in contact with SF CO2 was levelled to about 3. On t he other hand, below pH 3, the pH change is negligibly small. The distribut ion constant (K-D,K-SF CO2) of HMO(6)Q between SF CO2 and water at 20.4 MPa was about one tenth of the K-D for heptane - water system, indicating that the solubility of HMO(6)Q in SF CO2 is remarkably smaller compared with th at in heptane. The Ga(III)-HMO(6)Q and Ga(III)-HO(6)Q complex extracted int o SF CO2 were asigned to be Ga(OH)(MO(6)Q)(2) and Ga(O(6)Q)(3), respectivel y. Palladium(II) was extracted with HMQ as Pd(MQ)(2) from a weakly acidic s olution. Even in the the presence of HMQ, the Pd(II)-HMQ complex extracted from the higher HCl concentration should be H2PdCl4. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.