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

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