Some physico-chemical properties of D2EHPA Part 2.: Distribution, dimerization and acid dissociation constants in n-hexane/1 M (Na+,H+)SO42- system, interfacial adsorption and excess properties

From the distribution data for di-(2-ethylhexyl)phosphoric acid (D2EHPA, RH) between n-hexane and 1 M (Na+,H+)SO42-, the equilibrium constants of D2EHPA for dimerization, distribution and acid dissociation constants were determined as K-2 = 3.17 X 10(4) m(3)/kmol, K-d = 3.17 X 10(3) and K-a = 4.47 X 10(-2) kmol/m(3), respectively. Using the interfacial tension data, the cross-sectional areas (A) of D2EHPA molecules adsorbed at the interfaces were measured for the 1 M (Na+,H+)SO42--RH in different diluent systems and found to vary in the following order: cyclohexane (88.4 Angstrom(2)) < n-hexane (94.7 Angstrom(2)) < kerosene (113.7 Angstrom(2)) < carbon tetrachloride (137.8 Angstrom(2)) < o-xylene (172.4 Angstrom(2)) < toluene (186.3 Angstrom(2)) < benzene (207 Angstrom(2)) < chloroform (240 Angstrom(2)) < amyl alcohol (423 Angstrom(2)). This order has been correlated with the Ti(IV)-extraction data. The extraction of Ti(IV) was high when A was small. Interactions of D2EHPA with n-hexane, n-octane, cyclohexane, carbon tetrachloride, toluene and nitrobenzene were studied in terms of excess properties, i.e. excess molar volume (V-m(E)), excess viscosity (n(E)), excess Gibbs free energy of activation of flow (G E). Variation of these values and the interaction parameters (d) for D2EHPA-diluent binary mixtures showed that D2EHPA interacts with diluents in varying degrees. However, no correlation between d, G(E), eta(E) or V-m(E) and the metal extraction characteristics was noticed. (C) 2003 Elsevier Science B.V. All rights reserved.