Modeling plutonium sorption to kaolinite: Accounting for redox equilibria and the stability of surface species

Abstract

 Two pH-pe diagrams for Pu are drawn for (i) the solution and (ii) the surface. Pu sorption and redox speciation can be predicted. The redox potential is crucial information: it controls Pu overall sorption. This approach can be applied to other minerals and actinides.

Sorption and redox speciation of plutonium at the illite surface under highly saline conditions

“…As previously inferred for actinide uptake on clays, the redox speciation of actinides is influenced by the formation of surface complexes [21][22][23]. The Pu(IV)/Pu(III) borderline at the illite surface (denoted as {Pu(IV)/Pu(III)} surf ) is expected to depend on the individual Pu(IV) and Pu(III) sorption behavior [22][23], and can be calculated for = 0.1, 1.0 and 3.2 m (Fig.…”

“…When different Pu redox states coexist, the overall uptake of actinides on clays highly depends on pe [21][22][23]. As pointed out before, R d data scatter at acidic pH m , which might be due to slight variations in redox conditions in individual batch experiments.…”

“…the Pu(IV)/Pu(III) borderline at the illite surface is shifted to lower pe). According to this model, when the redox conditions (pH/pe) fall between {Pu(IV)/Pu(III)} aq and {Pu(IV)/Pu(III)} surf , Pu(III) prevails in solution whereas Pu(IV) prevails at the illite surface, and the overall Pu uptake by illite is intermediate to the individual uptake of Pu in the two distinct oxidation states [22,23].…”

“…The Pu(IV)/Pu(III) borderline at the illite surface (denoted as {Pu(IV)/Pu(III)} surf ) is expected to depend on the individual Pu(IV) and Pu(III) sorption behavior [22][23], and can be calculated for = 0.1, 1.0 and 3.2 m (Fig. 3) according to the following equation: (5) {Pu(IV)/Pu(III)} aq is the Pu(IV)/Pu(III) borderline in solution (i.e.…”

“…It has been shown, that the overall uptake of redox sensitive actinides and their redox speciation at mineral surfaces can be estimated by taking into account the uptake of the individual redox states and the measured redox potentials, i.e. the (apparent) electron activity, pe [21][22]. Using the 2 SPNE SC/CE model, previous work demonstrated the applicability of the approach to describe Pu uptake on illite under anaerobic conditions in 0.1 m NaCl, where the Pu(IV)/Pu(III) redox couple was involved [23].…”