Distribution (or partition) coefficients (D-x) of several chelating agents and cobalt-chelates between aqueous phases and SC CO2 were determined. beta-Diketones and dithiocarbamates fluorinated or not were the investigated chelating agents for cobalt. Different solute concentrations and different aqueous phase pH values were experienced for fixed operating conditions at 270 bar pressure and 50 degreesC temperature. The results obtained were compared with similar measurements performed with hexane as surrogate Of SC CO2. HFAAH distribution ratio is weaker than AAH when SC CO2 is the extracting solvent. Distribution coefficients of cobalt-chelates, CoAA(2) and CoHFAA(2), are roughly equal when the solvent is SC CO2. With hexane, CoAA(2) exhibits a higher distribution coefficient than CoHFAA(2). However, distribution ratios for cobalt beta-diketonates are very weak (10(-2)-10(-3)) because of their tendency to form hydrated chelates in aqueous medium. On the opposite, cobalt dithiocarbamates (CoDDC3 and CoFDDC3) are very stable under acidic conditions, which explains their distribution ratios much higher than 1. Hence, chelating agents NaDDC and LiFDDC seem to be more suitable than beta-diketonates to extract divalent cobalt from aqueous medium, in spite of their instability in an acidic medium formed by H2O in contact with SC CO2. (C) 2002 Elsevier Science B.V. All rights reserved.