Radionuclides colloid formation

Geckeis, H., Ngo Manh, T. H., Bouby, M. Kim, J. I. 2003. Aquatic colloids relevant to radionuclide formation characterization by size fractionation and ICP-mass spectrometric detection. Colloids and Surfaces A Physicochemical and Engineering Aspects, 217, 101-108. 

If colloids generated by waste package component interactions readily flocculate or are otherwise removed from solution soon after formation, they may not represent a waste management problem because colloidal transport of radionuclides would be limited. 

Sorption of radionuclides on particulates in solution is frequently observed. The particles may be coarsely or finely dispersed. Their surface properties (surface layer, charge, ion-exchange and sorption properties) play a major role. In general, they offer a great number of sorption sites on the surfaee, and microamounts of radionuclides may be found on the surface of these particles instead of in solution. Sorption of radionuclides on colloidal particles leads to formation of radioeolloids (carrier colloids, section 13.4). 

Colloids are found in many systems, e.g. in natural waters and in the air. Traces of colloids formed by dust particles or by particles given olf from the walls of containers are practically omnipresent. They can only be removed by careful ultrafiltration. If a radionuclide or a labelled compound enters such a system, there is a high probability that it will be sorbed on the colloids, provided that the competition of other ions or molecules is not too strong. Only if the presence of colloids from other origins can be excluded and if the solubilities of relevant species are not exceeded, formation of radiocolloids by microamounts of radionuclides can be neglected. 

Formation of intrinsic colloids in natural waters can be excluded for radioisotopes of elements of groups 0, I and VII, and the probability that they may be formed is small for radioisotopes of elements of other groups as long as the concentration of the elements is low. In general, formation of carrier colloids by interaction of radionuclides with colloids already present in natural waters is most probable. Thus, clay particles have a high affinity for heavy alkali and alkaline-earth ions, which are bound by ion exchange. This leads to the formation of carrier colloids with Cs, Ra and °Sr. Formation of radiocolloids with hydrolysing species has already been discussed (section 13.4). 

Due to the specificities of the RBS technique, model systems representative of colloids, heavy elements and surfaces encountered in natural systems relevant to radwaste disposal have been selected. Hence, investigations have been devoted to the study of i) colloids representative of those met in granitic or sedimentary formations (11, 16) such as silica, iron oxide and humic acids which may be considered as carrier colloids, ii) heavy elements as chemical analogues of radionuclides of interest such as Nd(III) or U(V1) as ionic species... 

---