Extraction mechanism of Gd3+ by BTMPPA

The extraction behavior of Gd(III) from acidic nitrate-acetato medium by bis(2,4,4-trimethylpentyl)phosphinic acid (BTMPPA, H2A2) in toluene either alone or in combination with trioctylphospine oxide (TOPO, B) has been investigated as a function of contact time, concentrations of Gd3+, H+, NO3− and Ac− (acetate) in the aqueous phase, the concentration of H2A2 and TOPO in the organic phase and temperature. Dependencies of H+, BTMPPA, TOPO and Ac− concentrations on extraction ratio suggest that the extracted species are [Gd(Ac)(HA2)2·H2A2] and [Gd(Ac)A2·HA·2B] for without and with TOPO, respectively at lower loading, while GdA3 is extracted at higher loading in both cases. The synergistic effect of TOPO is observed only at higher TOPO concentrations region. The equilibrium constants are evaluated to be 10−0.63 and 10−2.79 for the system without and with TOPO, respectively. The La(III)/Gd(III) separation factors are found to be 348 and 393 for the system without and with TOPO, respectively. The temperature dependence of the extraction data from acidic nitrate-acetato gives the enthalpy of extraction, 56 kJ/mol. The loading capacity for 100 g BTMPPA is found to be 17.89 g Gd(III).