Solubility measurements and sorption studies of thorium in cement pore water

Abstract

Solubility experiments and sorption studies were carried out with microcrystalline ThO 2 and alkaline cement pore waters. For fresh pore water, a solubility of 10 −9 M was found and for aged (portlandite, equilibrated) pore waters, 10 −10 M, which is expected in aqueous systems with elevated pH-values. Sorption experiments were carried out at cement to pore water ratios of 0.5 g/l, 5 g/l and 50 g/l with fresh and aged cement pore waters. With aged pore water the thorium-concentration in the aqueous solution was below the detection limit of 0.01 μg/l thorium for the experiments using 5 g/l and 50 g/l, which resulted in a lower limit for the k D-values of >48 m 3/kg and >4.8 m 3/kg, respectively. For the cement to pore water ratio of 0.5 g/l, the k D-value was 83.31±0.04 m 3/kg. With fresh cement pore water the k D-values for cement to pore water ratios of 5 g/l and 50 g/l were again below the detection limit and were about one order of magnitude smaller than for aged pore waters, i.e. >3.42 m 3/kg and >0.342 m 3/kg, respectively, and 19.5±0.6 m 3/kg for the cement to pore water ratio of 0.5 g/l.