The solubility and sorption of protactinium in the near-field and far-field environments of a radioactive waste repository

The solubility and sorption of protactinium have been studied for typical near-field and far-field chemical environments. The apparent solubility limit of protactinium in the near-field at pH 11 to pH 12 is about 10-10M. Sorption onto all of the solid phases studied is typically high, with values of RD ranging from 102 to 106 ml g-1. These values of RD vary with the hase separation technique used, the initial concentration of protactinium and the water to rock ratio employed. This variation in RD is in part attributable to the formation of large polymeric (or agglomerated) species under all the experimental conditions considered. (author)