The precipitation of gypsum, celestine, and barite and coprecipitation of radium during seawater evaporation

The removal of Ra commences in concordance with the precipitation of Sr and Ba, suggesting that Ra removal is controlled by the formation of a solid solution. Although a ternary solid solution of RaxBaySr1−x−ySO4 actually precipitates, the removal of Ra was modeled by the precipitation of a binary solid solution of RaxBa1−xSO4. Using empirical law from the literature, the removal of Ra could be modeled fairly well. The model suggests that the removal of Ra in evaporated seawater is hindered in comparison to low ionic strength solutions. This inhibition is a result of: 1. The high ionic strength (up to 10.8 mol kg−1); and 2. Precipitation kinetics that may be quantified by the degree of supersaturation with respect to end-member barite in the evaporated seawater (up to 51).