PhD thesis

Sorption and interfacial redox of Sn(II) under anoxic conditions


PhD student:
Siriwan Dulnee
Supervisor:
Dr. Andreas Scheinost (HZDR)
Division:
Molecular Structure
Period:
05/2010–04/2013


Motivation of work:

The presence of a long half-life Sn-126 (250,000 yr) from nuclear fission is a potential concern in nuclear waste management, so sorption and migration behavior needs to be well understood to predict its risk in a long term. But the redox state (di- or tetravalent) under the expected anoxic conditions is still a matter of debate., and thermodynamic speciation of Sn is still lacking of agreement in the exiting literatures especially under neutral pH and low Cl−. We therefore investigated the stability of Sn(II) in the presence of a highly redox-reactive mineral, magnetite (FeIIFeIII2O4), as functions of pH and time. The experiments were performed at < 2 ppm O2, and redox state and local structure was monitored over time by X-ray absorption spectroscopy (XAS).

Objectives:

  1. To study sorption behavior of Sn(II) on nano-magnetite as a function of pH and time.
  2. To study interfacial redox of Sn(II) by using active-redox magnetite.
  3. To model Sn surface complexation by Monte Carlo and nonlinear optimization program of PEST with PHREEQC.