Stabilities and thermodynamics of uranyl(II) and thorium(IV) complexes of 2-mercaptoethanol

The complexation of UO2+2 and Th+4 ions with 2-mercaptoethanol has been studied by potentiometric and conductometric titration techniques. Uranyl ion forms 1 : 1 and 1 : 2 complexes in the pH-range 3.3-6.5 and thorium ion forms 1 : 2, 1 : 3, and 1 : 4 complexes in the pH-range 3.2-4,8 with considerable overlapping. Their log ksub(stab). values are determined at 10, 20 and 300C at ionic strength μ=0.1M (NaClO4) by applying Calvin-Melchior's extension of the Bjerrum method. The overall changes in thermodynamic functions ΔG, ΔH, and ΔS accompanying complexation determined at 200C are -19.48kcal/mole, -22.77 kcal/mole, -11.23 cal/deg.mole for uranyl complexes and -33.94 kcal/mole, -4.93 kcal/mole, 99.00 kcal/deg. mole for thorium complexes, respectively. (author)