Nuclear volume effects in equilibrium stable isotope fractionations of mercury, thallium and lead

Abstract

The nuclear volume effects (NVEs) of Hg, Tl and Pb isotope systems are investigated with careful evaluation on quantum relativistic effects via the Dirac’s formalism of full-electron wave function. Equilibrium 202Hg/198Hg, 205Tl/203Tl, 207Pb/206Pb and 208Pb/206Pb isotope fractionations are found can be up to 3.61‰, 2.54‰, 1.48‰ and 3.72‰ at room temperature, respectively, larger than fractionations predicted by classical mass-dependent isotope fractionations theory. Moreover, the NVE can cause mass-independent fractionations (MIF) for odd-mass isotopes and even-mass isotopes. The plot of vs. for Hg-bearing species falls into a straight line with the slope of 1.66, which is close to previous experimental results. For the first time, Pb4+-bearing species are found can enrich heavier Pb isotopes than Pb2+-bearing species to a surprising extent, e.g., the enrichment can be up to 4.34‰ in terms of 208Pb/206Pb at room temperature, due to their NVEs are in opposite directions. In contrast, fractionations among Pb2+-bearing species are trivial. Therefore, the large Pb fractionation changes provide a potential new tracer for redox conditions in young and closed geologic systems. The magnitudes of NVE-driven even-mass MIFs of Pb isotopes (i.e., ) and odd-mass MIFs (i.e., ) are almost the same but with opposite signs.

Nuclear field shift effects on stable isotope fractionation: a review

“…These authors all found that the nuclear field shift effect was the dominant controlling factor for isotope fractionation of the heavy elements, far more important than the conventional mass-dependent effects. Anomalous light isotope enrichments of U(IV), U(VI), Pb(II) and Tl(I) relative to U(III), U(IV), Pb 0 and Tl 0 were found (Schauble 2007;Abe et al 2008aAbe et al , b, 2010Fujii et al 2011aFujii et al , 2013Yang and Liu 2015). In addition, zinc (Fujii et al 2009c and nickel isotopes (Fujii et al 2011b) were studied both experimentally and theoretically.…”

“…These authors found that the NFSE-driven MIFs of odd mass number isotopes (D (Yang and Liu 2015) if using the nuclear charge radii of Fricke and Heilig (2004). It agreed well with the experimental results.…”

“…The calculation of Schauble (2007), Wiederhold et al (2010), Ghosh et al (2013) and Yang and Liu (2015) all showed that a part of the MIFs of Hg-bearing species are caused by the nuclear field shift effect. These authors found that the NFSE-driven MIFs of odd mass number isotopes (D (Yang and Liu 2015) if using the nuclear charge radii of Fricke and Heilig (2004).…”

“…So far, there have been only a few NFSE-included fractionation factors that are determined by theoretical calculations, such as those for uranium, lead, mercury and thallium isotopes (Abe et al 2008a(Abe et al , b, 2010Fujii et al 2011a;Schauble 2007;Wiederhold et al 2010;Ghosh et al 2013;Fujii et al 2013;Yang and Liu 2015) (Fig. 4b-f).…”

“…(6) can be simplified as follows: ]. d The NFSE-driven fractionations of the Pb-bearing species, relative to Pb 0 (Yang and Liu 2015), and Pb 2? (Fujii et al 2011a, b).…”