Evidence and characterization of silica-containing colloids of the tetravalent actinides Th, U and Np
For predicting the migration behaviour of heavy metals released from radioactive waste repositories, detailed knowledge of the chemical and physical character of these elements is required. The actinides are expected to be tetravalent under the anoxic conditions of a repository. Due to their low solubilities tetravalent actinides are normally regarded as immobile on the water path.
Nevertheless, sparingly soluble species can be mobilized by the formation of colloids. One possibility of colloid formation is the co-precipitation of the actinides with ubiquitous water components like silicate.
For U(IV) and Th(IV) there has been evidence for the formation of silica-containing waterborne nanoparticles at near neutral pH. For Np(IV) it is still missing.
The aim of this work is the characterization of such silica-containing actinide colloids by investigating their properties, e.g. particle size distribution, surface charge, inner structure, long-term stability. Furthermore, the influence of ambient conditions such as salt concentration or presence of microorganisms on the formation and the properties of the actinide(IV) colloids is to be elucidated.