Kinetic Speciation of Co(II), Ni(II), Cu(II), and Zn(II) in Model Solutions and Freshwaters:  Lability and the d Electron Configuration

Abstract

The kinetic speciation of Co(II), Ni(II), Cu(II), and Zn(II) in model solutions of a well-characterized fulvic acid (Laurentian fulvic acid), freshwater samples from the Rideau River (Ottawa, Ontario), and freshwater samples from the Sudbury (Ontario) area were investigated by the competing ligand exchange method using Chelex 100 as the competing ligand and by inductively coupled plasma-mass spectrometry to measure the dissociation kinetics. The metal species were quantitatively characterized by the rate coefficient for the first-order dissociation of metal complex to free metal ion. This technique can be applied to almost all elements and represents an important advance in our ability to investigate the kinetic availability of metal species in the freshwater environment. The order of the lability of the metal complexes, Co(II) > Ni(II) > Cu(II) < Zn(II), follows the reverse order of the ligand field stabilization energy with the exception of Cu(II); the behavior of Cu(II) is also due to the Jahn-Teller effect, which shortens the equatorial bonds and lengthens the axial bonds of a tetragonally distorted Cu(II)-L6 complex. This study has demonstrated a relationship between the lability of metal-DOM complexes of the 3d transition metals in freshwaters and their d electron configuration. This is the first time that the importance of the d electron configuration on the lability of metal complexes in the freshwater environment has been demonstrated. The slow complexation kinetics of both Ni(II) and Cu(II) suggestthatthe usual equilibrium assumption for freshwaters may be invalid.

Dissolved cobalt speciation and reactivity in the eastern tropical North Atlantic

“…log K Co(II)EDTA = 16.45 vs. log K Co(III)EDTA = 41.4 (Martell and Smith, 1976)). In addition, strong octahedral Co(III) complexes are kinetically inert while Co(II) complexes are usually very labile (Soni and Soni, 2013), although slow Co(II) dissociation kinetics have been reported in some freshwater samples (Collins and Kinsela, 2010;Sekaly et al, 2002). Consequently, it is likely that the labile Co pool contains Co(II) species while the inert Co pool may include Co(III) or particularly inert Co(II) species.…”

Speciation of nickel in surface waters measured with the Donnan membrane technique

“…In earlier studies slow dissociation kinetics 80 of natural Ni-DOM complexes have been demonstrated [6,10,[13][14][15][16], however no data were 81 found on association kinetics. We used the Donnan speciation technique [17], a method which 82 minimizes the disturbance of the equilibrium composition in the test solution and which does 83 not rely on a priori knowledge of the conditional stability constant of a competing ligand.…”

Kinetic Study of Chromium (III) - PVP Complex by using Radio-Tracer Technique

“…A weighed amount of chromium nitrate, Cr(NO 3 ) 3 .9H 2 O salt has been subjected to neutron irradiation in the CIRUS reactor,BARC,Mumbai with a neutron flux 1 x 10 12 n.cm -2 .s -1 .The nuclear reaction for the production of chromium radionuclide is 50 Cr(n,ϒ) 51 Cr.The half-life of 51 Cr is 27.7days and the ϒ-ray energy is 320.08 KeV. After irradiation the salt is dissolved in deionised water.…”