SOLUBILITY MEASUREMENTS AND SORPTION STUDIES OF THORIUM IN CEMENT PORE-WATER

Solubility experiments and sorption studies were carried out with micr ocrystalline ThO2 and alkaline cement pore waters. For fresh pore wate r, a solubility of 10(-9) M was found and for aged (portlandite, equil ibrated) pore waters, 10(-10) M, which is expected in aqueous systems with elevated pH-values. Sorption experiments were carried out at ceme nt to pore water ratios of 0.5 g/l, 5 g/l and 50 g/l with fresh and ag ed cement pore waters. With aged pore water the thorium-concentration in the aqueous solution was below the detection limit of 0.01 mu g/l t horium 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, resp ectively. For the cement to pore water ratio of 0.5 g/l, the k(D)-valu e was 83.31+/-0.03 m(3)/kg. With fresh cement pore water the k(D)-valu es for cement to pore water ratios of 5 g/l and 50 g/l were again belo w the detection limit and were about one order of magnitude smaller th an for aged pore waters, i.e. >3.42 m(3)/kg and >0.342 m(3)/kg, respec tively, and 19.5+/-0.6 m(3)/kg for the cement to pore water ratio of 0 .5 g/l. (C) 1998 Elsevier Science S.A.