Colloidal silica, silica sol, is being used in the underground rock characterization facility ONKALO in Olkiluoto, Finland, for the sealing of the fractures of the hydraulic apertures less than 0.05 mm. The use of all colloidal material has to be considered in the long–term safety assessment of a spent nuclear fuel repository. The objective of this work was to follow the stability of silica colloids released from the gelled silica sol. Release and stability of silica colloids was studied in reference groundwaters, low salinity Allard and saline OLSO which simulates Olkiluoto conditions. Sodium and calcium chloride solutions and deionized water were used to study the stability of silica colloids as a function of ionic strength. The stability of colloids has been followed so far six years by measuring particle size distribution, colloidal silica concentration and zeta potential using dynamic light scattering. In the Allard water and in the most diluted sodium and calcium chloride solutions, the mean particle diameter has been rather constant at about 100 nm over the entire experimental time period. The highly negative zeta potential values have been indicated the existence of stable silica colloids. In the OLSO water and in 0.1 – 1 M sodium chloride and 0.03 – 3 M calcium chloride, the mean particle diameter has been increased during the experiment and the particle diameter has varied from nanometers to thousands of nanometers. Zeta potential values have been near zero, and an increase in particle size followed by the disappearance of large particles is an indication of particle flocculation or coagulation and unstable colloidal dispersion. Results confirmed that the stability of colloids depends significantly on the groundwater salinity. Under the prevailing saline groundwater conditions in Olkiluoto, silica colloids are instable, but the possible change in salinity e.g. due to glacial melt waters has to be considered.
|Otsikko||WM2014 Conference Proceedings|
|Tila||Julkaistu - 2014|
|OKM-julkaisutyyppi||A4 Artikkeli konferenssijulkaisuussa|
|Tapahtuma||WM2014 Conference - Phoenix, Arizona, Yhdysvallat (USA)|
Kesto: 2 maaliskuuta 2014 → 6 maaliskuuta 2014
- 116 Kemia