Partition coefficient of Ra in witherite.

The heterogeneous partition coefficient ( λ) for Ra in BaCO (witherite) was determined by coprecipitation using the free drift method. Initially, CO (100 %) was bubbled through a solution equilibrated with witherite. After a small amount of Ra was added into the solution, coprecipitation was induced by a slow increase in pH, caused by degassing CO(g) from the solution. Kinetically controlled precipitation was restricted to be slow because of the slow degassing of CO(g). The observed low precipitation rate allowed for the equilibrium partitioning of elements during coprecipitation of witherite. The value of λ derived for Ra was (1.3 ± 0.7) × 10, a value similar to that obtained from the coprecipitation of Ra in CaCO (calcite). The obtained results indicated that partitioning of Ra in carbonate-based minerals was not dependent on the similarity of its ionic radius with that of the metal in the host carbonate. [ABSTRACT FROM AUTHOR]