Supercritical carbon dioxide extraction equilibrium of gallium(III) with 2-methyl-8-quinolinol and 2-methyl-5-butyloxymethyl-8-quinotinol

This work performed fundamental studies for the extraction of gallium(III) with 2-methyl-8-quinolinol (HMQ) and 2-methyl-5-butyloxymethyl-8-quinolinol (HMO(4)Q) into supercritical carbon dioxide (SF-CO2) from a weakly acidic solution. The distribution constants of HMO(4)Q between aqueous and SF-CO2 phases were determined at 45 degreesC, 8.6-20.4 MPa and I = 0.1 M (H, Na)NO3 (M = mol dm(-3)). At 45 degreesC and 15.7 MPa, gallium(III) was hardly extracted with HMQ into SF-CO2, but was quantitatively extracted with HMO(4)Q in the pH range of 2.20-2.84. The extraction constant, K-ex,K- (SF-CO2) (= [Ga(OH)(Mo(4)Q)(2)](SF-CO2)[H+](3)[Ga3+](-1)[HMO(4)Q](SF-CO2)(-2)), of gallium(III) with HMO(4)Q was determined to be 10(-2.6+/-0.1) at 45 degreesC, 15.7 MPa and I = 0.1 M (H, Na)NO3, which was 63 times larger than that in heptane at 45 degreesC and 0.10 MPa. It was also found that the addition of 3,5 -dichloro phenol as a synergist enhanced the extractability of gallium(III) with HMO(4)Q into SF-CO2. (C) 2002 Elsevier Science B.V. All rights reserved.