Np(V) uptake by bentonite clay: Effect of accessory Fe oxides/hydroxides on sorption and speciation

- Iron oxyhydroxide dominates the Np(V) sorption at trace concentration onto raw clay.
- Accessory minerals in clay effect on pH edge and kinetics of Np(V) sorption.
- SCM was applied to describe sorption of Np(V) onto raw clay samples.

Batch sorption experiments on thoroughly characterized bentonites and thermodynamic modeling studies were conducted to reveal the role of iron-containing accessory phases on the interfacial behavior of Np(V). Bentonite clays from different industrial deposits with varying total iron contents were selected for the studies. The samples were characterized by XRD, Mossbauer spectroscopy, XRF, HRTEM, SEM-EDX and other techniques, and wherever possible, the accessory iron phases were identified and quantified. Thermodynamic modeling using available surface complexation data revealed the dominant role of the goethite accessory phase, which was present as nanoparticles, in Np(V) sorption at trace level concentrations (10−14 M). This fact is independently supported by the combination of SEM-EDX and α-track radiography. These studies illustrate the important role that accessory minerals can play in radionuclides sorption data. This is important to the understanding and modeling of the molecular-level speciation of radionuclides.

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