(BaxSr1-x)SO4 coprecipitates are ubiquitous in natural and industrial processes. However, knowledges of heterogeneous (BaxSr1-x)SO4 precipitation at organic-water interfaces are very limited. Herein, glass coated with self-assembled thin films terminated with mixed sulfhydryl (-SH) and carboxyl (-COOH) functional groups was used as model organic-water surfaces for heterogeneous (BaxSr1-x)SO4 precipitation. The in-situ real-time observations of heterogeneous precipitation revealed that the formation of (BaxSr1-x)SO4 was a nucleation dominated process even if bulk condition was undersaturated with respect to both BaSO4 and SrSO4. The interactions between organic surfaces and ions were investigated through batch adsorption experiments. Strong adsorption of cation ions (e.g. Ba2+ and Sr2+) onto organic surfaces occurred, leading to have the local solutions near substrate much more supersaturated than the bulk solution, which promoted the heterogeneous nucleation. Interestingly, quite different from the formation of Sr-poor (BaxSr1-x)SO4 (x≈1) homogeneous precipitates in solutions with varying Ba2+/Sr2+ ratios, significant amounts of Sr incorporation in heterogeneous (BaxSr1-x)SO4 precipitates on substrates were observed with x values ranging from 0.07 to 0.92. From viewpoints of both thermodynamics and kinetics, the favored compositions (i.e., x) of homogeneous and heterogeneous precipitates were calculated using solid solution nucleation theory. The higher incorporation of Sr in heterogeneous precipitates than in homogeneous precipitates was caused by faster nucleation rate at organic-water interfaces than in bulk solution. This study provided novel insights on the mechanisms of heterogeneous BaxSr1-x)SO4 nucleation at organic-water interfaces, which can help better understand and control the formation of (BaxSr1-x)SO4 in natural and engineered settings.

Heterogeneous (BaxSr1-x)SO4 nucleation at organic-water interfaces: Implications for strontium immobilization

255th National Meeting (2018)

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