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 K2=3.17×104 m3/kmol, Kd=3.17×103 and Ka=4.47×10−2 kmol/m3, 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 Å2)<n-hexane (94.7 Å2)<kerosene (113.7 Å2)<carbon tetrachloride (137.8 Å2)<o-xylene (172.4 Å2)<toluene (186.3 Å2)<benzene (207 Å2)<chloroform (240 Å2)<amyl alcohol (423 Å2). This order has been correlated with the Ti(IV)-extraction data. The extraction of Ti(IV) was high when A was small. ctions 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 (VmE), excess viscosity (ηE), excess Gibbs free energy of activation of flow (GE). 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, GE, ηE or VmE and the metal extraction characteristics was noticed.