Co-precipitation is a simple, inexpensive, and effective method for the removal of radionuclides, metals, and metalloids from industrial wastewaters. In a co-precipitation 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 co-precipitation due to its low solubility, stability, and ability to incorporate a large number of both cations and anions (Sr2+, Ra2+, Pb2+, HAsO42-, CrO42-, SeO42-). While 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 explored how saturation index and other solution conditions such as ionic strength, cation/anion ratio, and solid/liquid ratio affect the incorporation of strontium into barite. X-ray fluorescence nanospectroscopy conducted at the Hard X-ray Nanoprobe (HXN) beamline at National Synchrotron Light Source II (NSLS-II) enabled nanoscale-resolution mapping of chemical composition within individual barite particles. We observed that particles precipitated at lower saturation index have much greater variability in size, morphology, and strontium content while particles precipitated at higher saturation index are much more uniform. In particles precipitated at high saturation index, we observed less strontium uptake than predicted by thermodynamic theory while at low saturation index we observed more strontium uptake. We surmise that as saturation index increases, both the nucleation and growth rates increase, creating conditions for uniformly low Sr uptake during precipitation. At lower saturation index, slower precipitation results in particles forming under a wider range of aqueous concentrations and consequently exhibit heterogeneity in Sr uptake and sometimes very high levels of Sr uptake. These observations further our understanding of solid solution-aqueous solution systems and point towards reducing saturation index through careful control of the sulfate dose as a method for maximizing strontium removal from barium and strontium contaminated wastewaters such as flowback water from the hydraulic fracturing of shales.

Strontium removal from wastewater through co-precipitation with barite

256th National Meeting (2018)

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