Kinetics of extraction of Zr(IV) from chloride solution after 30-day ageing by D2EHPA using the single drop technique

The kinetics of solvent extraction of Zr(IV) from acidic chloride solution by D2EHPA have been investigated by the single drop technique after 30-day ageing of the aqueous phase. The flux equations at 303 K have been derived for three aqueous acidities of 0.10, 1.00 and 5.00 M HCl, respectively, as: J (kmol/m2 s)=10−4.57(1+0.00036[Zr(IV)]−1)−1[H+][H2A2](0); J (kmol/m2 s)=10−4.86(1+0.0056[Zr(IV)]−1)−1[H2A2](0) and J (kmol/m2/s)=10−5.46(1+0.0056[Zr(IV)]−1)−1[H+][H2A2](0). The values of activation energy (Ea) depend on the Zr(IV) concentration and temperature regions. The values of Ea, ΔH±, ΔS± have been determined under various conditions. The flux equations and the values of Ea indicate that the extraction processes are chemically controlled at lower temperature and Zr(IV) concentration regions. The reacting Zr(IV) species that satisfy the rate data are either [Zr8(OH)20(H2O)24Cl13]− or [Zr4(OH)8/9(H2O)16Cl9/8]− in 0.10 M HCl; [Zr4(OH)8(H2O)16Cl8] or Zr(OH)Cl3 in 1 M HCl and [Zr(H2O)4Cl4]2− in 5 M HCl. On the other hand, at higher temperature and Zr(IV) concentration regions, extraction processes are diffusion controlled, where the rates of diffusion of H3A2+ are slower than the rates of diffusions of [Zr8(OH)20(H2O)24Cl13]−, [Zr4(OH)8(H2O)16Cl8] and [Zr(H2O)4Cl4]2− in 0.10, 1 and 5 M HCl media, respectively.