Extraction of chromium (Cr(VI)) from the aqueous acidic solution into a co-existing organic phase containing Alamine 336 (C-8-C-10 tertiary amine mixture) and diluent (xylene) was studied at isothermal condition (298.2 K). The distribution ratio was measured for two initial aqueous concentrations of Cr(VI), i.e. 0.019 mol/dm(3) (1 mg/ml) and 0.192 mol/dm(3) (10 mg/ml) against various molarities of the aqueous phase sulphuric acid in the range from 0.05 to 4 mol/dm(3). The overall loading factor of amine (Z(t)) exhibits a maximum restricted between the aqueous phase acidity of 0.75-1 mol/dm(3) H2SO4 for a lower amine concentration related to the ratio of initial concentrations of amine to Cr(VI),C-NH3(degrees)/C(CR(VI))degrees approximate to 0.75 or less than this limit. In the range above this value a continual decreasing of Z(t) has been observed. A comparative study of the extraction degrees of Cr(VI) by Alamine 336 and Aliquat 336 extractants for the pH range of 1-7 has been evaluated. The results were correlated using various versions of the mass action law, i.e. a chemodel approach and a modified version of the Langmuir equilibrium model comprising the formation of only one type Cr(VI)-amine aggregated structure. (C) 2003 Elsevier B.V. All rights reserved.