PhD thesis

Investigations of anionic influences upon the interactions of trivalent lanthanides and actinides with the secondary mineral phase calcite

Pic Hofmann

PhD student:
Sascha Hofmann
Prof. Dr. T. Stumpf (HZDR)

For the safety assessment of a high level nuclear waste disposal, the intrusion of ground water is considered the worst case scenario. Geochemical processes play a major role as retentive mechanisms for radionuclides. These can be removed from an aqueous solution by sorption on primary mineral phases or be even incorporated during the growth of secondary phases such as calcite CaCO3. Trivalent lanthanide and actinide ions can form so-called solid solutions in this host structure in combination with Na+ for charge balance. However, these systems were studied under artificial conditions, using NaClO4 as background electrolyte. The influence of relevant anions like CO32−, OH, F, Cl, Br or NO3 is quite unknown and therefore subject to this doctorate.

For these studies, experimental methods involving microscopic (AFM, SEM), spectroscopic (TRLFS, XRD, CTR/RAXR, EXAFS) and analytic (ICP-MS, ICP-OES, IC) techniques are used. A rather unexpected but strong (negative) influence of NaNO3 on the calcite surface and respective sorption and incorporation reactions could already be shown.

These investigations aim at molecular processes in realistic systems in order to improve the understanding of geochemical surface processes.

This work is part of the German Federal Ministry of Education on Research (BMBF) joint project ImmoRad for “Fundamental investigations for the immobilization of long-lived radionuclides through interaction with secondary mineral phases in deep geological nuclear waste repositories”. Project's webpage: