NUCLEATION, GROWTH, AND CRYSTAL MORPHOLOGY OF SR CO-PRECIPITATION INTO BARITE (Invited Presentation)

Ion co-precipitation into solid solutions has important applications in radioactive waste storage and industrial wastewater treatment. The co-precipitation of ions like Sr into barite by the direct addition of Na₂SO₄ is one cost-effective method of treating contaminated waters. However, thermodynamic solid solution theory often under-predicts trace ion removal. We have developed a geochemical model that nucleates and grows barite particles while incorporating Sr into each growing surface layer. The model also examines simple crystal morphologies, including flat squares and flat disks. Simulations at a low barite saturation index (SI) of 2.34 were compared with simulations at the higher SI of 3.80. At the higher SI, barite particles were more uniform in particle size and contained low quantities of Sr throughout most of the particle. Simulations at the lower SI had larger variability in particle size, along with higher overall quantities of Sr in the solid. These findings agree with experiments by Hunter et al. (2020), in which, at SI 3.80, co-precipitated (Sr,Ba)SO₄ particles were ~6 µm in size, while at SI 2.34, particles ranged from ~2 – 8 µm. When examining crystal morphology in our simulations, we found that flat disks removed slightly less Sr than flat squares due to differences in surface availability for ion attachment. The model can also be used to optimize metal removal conditions for wastewater treatment. For instance, the model predicts that increasing the amount of Na₂SO₄ added can also increase Sr removal. Further, our model can more accurately predict Sr removal than solid solution-aqueous solution thermodynamic theory.