Extraction and characterisation of colloids in waste repository leachate
thesisposted on 04.10.2012, 11:56 by Karen E. Verrall
Inorganic colloids are ubiquitous in environmental waters and are thought to be potential transporters of radionuclides and other toxic metals. Colloids present large surface areas to pollutants and contaminants present in waters and are therefore capable of sorbing and transporting them via groundwater and surface water movement. Much research has been and is currently being undertaken to understand more fully the stability of colloids in different water chemistries, factors which affect metal sorption onto colloids, and the processes which affect metal-colloid transport. This thesis first investigates ground water and surface water sampling and characterisation techniques for the investigation of the colloids present in and around a low-level waste repository. Samples were collected anaerobically using micro-purge low-flow methodology (MPLF) and then subjected to sequential ultrafiltration, again anaerobically. After separation into size fractions the solids were analysed for radiochemical content, colloid population and morphology. It was found that colloids were present in large numbers in the groundwaters extracted from the trench waste burial area (anaerobic environment), but in the surface drain waters (aerobic environment) colloid population was comparable t6 levels found in waters extracted from' above the trenches. There was evidence that the non-tritium activity was associated with the colloids and particulates in the trenches, but outside of the trenches the evidence was not conclusive because the activity and colloid concentrations were low. Secondly this thesis investigates the stability of inorganic colloids, mainly haematite, in the presence of humic acid, varying pH and electrolyte concentrations. The applicability of the Schulze-Hardy rule to haematite and haematitelhumic acid mixtures was investigated using photon correlation spectroscopy to measure the rate of fast and slow coagulation after the addition of mono, di and trivalent ions. It was found that humic coated colloids follow the Schulze-Hardy rule for mono and divalent cations, with the exception of copper ions. Trivalent ions do not follow the Schulze-Hardy rule because of their relatively strong complexation with humates. It was also found that the size of the ion has an effect on destabilisation, irrespective of charge.