JRP CALL information
Supported By

European Commission

Short description of the work
The corrosion of steel canister in a deep HLW repository may form iron (hydr)oxides upon contact with ground water. The formation of such corrosion phases can significantly delay the radionuclide migration to the far field. The immobilization can either occur by surface retention and/or by incorporation in the bulk structure. In a previous Actinet Joint Research Project (JRP), green rust (GR) and magnetite have been prepared in the presence of various lanthanides (La, Nd, Lu) and actinide (Am) and the solid phases were characterized by various methods. The GR transformation into magnetite by washing the suspension was not conclusive based on XRD and Raman spectroscopy data. In this JRP, we first tried to optimize the formation of GR then its transformation to magnetite.

The initial method to synthesise GRCl – coprecipitation of a mixture of Fe(II) and Fe(III) with Fe(II)/Fe(III)=5 and OH/Fetot= 1.25 – led to the presence of GRCl but also Fe2(OH)3Cl. Trials to optimize this method by varying the iron ratio or the base to total iron ratio led to the conclusion that magnetite was always present in the suspension. The lesser amounts were obtained for Fe(II)/Fe(III)=5 and OH/Fetot=1.25 although it was not detectable by XRD. Fe2(OH)3Cl still formed.

The formation of magnetite via GRCl as intermediary phase, by forming ferrihydrite first and reacting it with Fe(II) while maintaining the pH constant at 9, gave probing results. SEM of a sample taken 5 minutes after reaction showed the simultaneous presence of GRCl and magnetite. XRD only confirmed magnetite being present – the sample having possibly transformed before being prepared for XRD. Fe2(OH)3Cl was not dectected.

This aforementioned method could constitute a better alternative method to i) study the interaction of lanthanides/actinides with GRCl; ii) study their fate while the mixed valence compound transforms to magnetite and iii) avoid the formation of Fe2(OH)3Cl. The transformation of GRCl to magnetite was however relatively fast (< 1hour). The stage where GRCl dominates could be prolonged by first raising and keeping the pH of the ferrihydrite+ Fe(II) suspension to pH 7. After an hour or so, the pH would be finally raised to 9. XRD will be needed though to check if with the conditions Fe(II)/Fe(III)=0.5, only GRCl can be obtained at pH 7. According to Sumondour et al, only GRSO4 was detected at pH 7 but we are dealing here with GRCl more reactive and more prone to transform to magnetite.

References

A. Sumoondur*,S. Shaw,I. Ahmed and L. G. Benning, Green rust as a precursor for magnetite; an in situ synchrotron based study (in Geochemistry of the Earth's surface ), Mineralogical Magazine (February 2008), 72 (1):201-204

Main visitor contact data
Name: Dr. Sorin Nedel
Organisation: University of Copenhagen

JRP Identification
JRP nr: TALI-C01-13
JRP title: Structural elucidation of trivalent actinides retention by iron (hydr)oxides
JRP scope: Scope 2: Actinide in the geological environment

Visited Associated Pooled Facility
Visited APF during the stay: KIT-INE - Laboratories
Name of the APF Contact Person: Thorsten Schäfer

Other APF and organisation involved in the JRP
Other organisations involved:
Other APF involved in the project: CEA - DPC, KIT-INE - Beamline

Description of the work done at the associated pooled facility
Start date of the stay: 1/13/2014
End date of the stay: 1/24/2014
Quantity of access: 10
Access Unit: Days
Misc.: