Coprecipitation is a simple, inexpensive, and effective method for the removal of radionuclides, metals, and metalloids from industrial wastewaters. In a coprecipitation reaction, similarities in charge, size, and coordination chemistry allow a minor ion to substitute for a major ion within the crystal lattice of a newly formed solid. Barite (BaSO4) is an ideal host mineral for coprecipitation due to its low solubility and ability to incorporate a large number of both cations and anions (Sr2+, Ra2+, Pb2+, HAsO42-, CrO42-, SeO42-). While solid solution – aqueous solution (SS-AS) thermodynamic theory describing equilibrium for such solid solutions is well developed, poorly-understood kinetic processes limit the extent to which this theory is effective in predicting solid-aqueous partitioning. In this study, we compare experimental measurements of strontium incorporation into barite to SS-AS thermodynamic predictions for a range of initial saturations, salinities and cation/anion ratios. In every experiment we found more strontium incorporation than predicted by SS-AS thermodynamic theory, indicating the formation of metastable solid solutions. We found that kinetic models of coprecipitation based on classical nucleation theory performed better than SS-AS thermodynamic models but did not completely describe the observed trends. We developed a population balance model of homogeneous precipitation of barite from solution and by calibrating the model to experimental particle size distributions and UV-vis absorbance measurements, obtained barite nucleation and growth rates. We found that nucleation and growth rates both increase with increasing saturation, but at different rates. By linking Sr incorporation to the growth rate rather than the nucleation rate we were able to better match our experimental observations. Such kinetic models of coprecipitation will be useful to determine the optimal sulfate dose and cation/anion ratio to maximize strontium removal from barium and strontium contaminated wastewaters such as flowback water from the hydraulic fracturing of shales.

Kinetic processes in strontium removal from wastewater through coprecipitation with barite

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.