Partition coefficient of Ra in witherite

Yoshida, Yasushi*; Nakazawa, Toshiyuki*; Yoshikawa, Hideki

A heterogeneous partition coefficient for Ra in BaCO (witherite) was determined from a coprecipitation experiment using the free drift method. The initial solution was bubbled with 100% CO(g) and equilibrated with witherite. After a small amount of Ra was added into the solution, a coprecipioitation reaction was induced by increase of pH caused by degassing of CO (g). A kinetic reaction of precipitation was restricted to be slow due to slow degassing of CO(g). Precipitation rate was observed to be enough low comparing with values of low precipitation rates to derive equilibirium partitioning of elements in coprecipitation experiments with CaCO (calcite). The -value derived for Ra was = (1.30.7)10. This value was similar to that of Ra in CaCO (calcite). It indicated that partitioning behavior of Ra in carbonate minerals did not depend on affinity in radius of a cation in host carbonate.