Browsing by Author "Tikkanen, Otto"

The distribution coefficients of radium in Olkiluoto potassium rich biotite were obtained by batch sorption experiments carried out as a function of the concentration of radium and barium. The batch sorption experiments were carried out with four different Olkiluoto associated reference groundwater types: fresh mildly reducing granitic reference groundwater ALLMR (or modified Allard granitic water), glacial anoxic meltwater OLGA, carbonate containing reducing brackish reference groundwater OLBA, and saline reducing reference groundwater OLSR. The main focus of the experiments was to evaluate the effect of the water salinity on the sorption of radium on biotite. The results were compared with sorption results obtained in previous studies done on radium and radium’s physicochemical analogue barium. According to the sorption results, the distribution coefficients of radium on biotite were largest in lower salinity waters. As the barium concentrations of the sorption solutions were increased, the distribution coefficients of radium generally stayed level until they decreased noticeably in the higher studied Ba concentrations (10E-3 and 10E-4 mol/l). This suggests that radium is a poor competitor in the ion exchange adsorption interactions on the surface of biotite, when other cations are present in the solution. As a unique case amongst the more predictable reference groundwaters, the brackish OLBA behaved differently. Despite the increasing salinity of the sorption solutions, the apparent sorption of radium increased steadily throughout the barium isotherm. It was concluded that the high concentration of sulphate in the OLBA reference groundwater caused the occurrence of coprecipitation of radium with the added barium and sulphate as (Ba,Ra)SO4.