Marine barite cycling was important for rebuilding geochemical evolution and microbial metabolisms in paleoenvironments. However, occurance of marine barite in globally barite-understaturated oceans and enrichment of Sr remains paradoxical. In natural and engineered systems, barite (BaSO4) can precipitate from supersaturated solution as homogeneous precipitates in bulk solution and on substrates (e.g., rocks, equipment and facilities) as heterogeneous precipitates. Barite precipitation starts with nucleation followed by subsequent particle growth, during which impurity ions (e.g., Sr, Ra) can incorporate in the structure coprecipitate. Here homogeneous and heterogeneous (BaxSr1-x)SO4 precipitation in solution and on mixed thiol (-SH) and carboxyl (-COOH) coated SiO2 was studied. Heterogeneous (Bax, Sr1-x)SO4 nucleation occured even when the bulk solution was understaturated, due to enrichment of Ba and Sr ions onto the organics leading to higher local supersaturation. Significant amounts of Sr incorporation (x = 0.28-0.93) in the small heterogeneous nuclei (~ 1.5-4 nm) occured, consistent with predictions of solid solution nucleation. In bulk solution, fast growth of homogeneous precipitates occured leading to the formation of micrometer-sized crystals with little Sr incorporation (x ≈ 1), consistent with predictions of solid solution growth. New insights and explanations were provided here for marine barite formation and Sr incorporation in organic-abundant microenvironments in the water column and sediment of seawater.

Uncovering the mysteries of (Ba, Sr)SO4 in oceans: Heterogeneous nucleation of solid solution on organics

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.