Understanding sorption behavior of ions at the mineral-water interface is important to determine the fate of heavy metals in the environment. We used barite as a model substrate to understand heavy metal interactions with ionic crystals. The coverage and location of lead (Pb) sorbed to the (001) and (210) surfaces were studied as a function of aqueous Pb concentration using <i>in situ</i> specular x-ray reflectivity (XR) and resonant anomalous x-ray reflectivity (RAXR). For both surfaces in the absence of Pb, bariums and sulfates move small distances (&lt; 0.15 Å) from their bulk lattice positions and waters adsorb to compensate for missing bonds created during formation of the surface. At [Pb] = 6 – 100 µM, there are small differences in the interfacial structures for both surfaces, primarily in the top 3 Å of the crystal. At [Pb] ≥ 225 µM, the (001) interfacial structures are significantly distorted, especially within the top 5 Å of the crystal and 7 Å of the solution near the surface. At the (210) surface, interfacial distortions are smaller and occur in the top 3 Å of the crystal. These changes in the interfacial structures in the presence of Pb imply Pb sorption. Using RAXR, Pb sorption was measured at the (001) and (210) interfacial surfaces. At the (001) surface, Pb sorption increases as a function of Pb in solution and is best described by an incorporated species and an adsorbed species. The adsorbed fraction increases more rapidly than the incorporated fraction with increasing [Pb]. Atomic force microscopy images suggest the presence of a precipitated phase, which is resistant to removal in Pb free barite saturated solution. At the (210) surface, Pb sorption is best described using a single incorporated species, the coverage of which increases with increasing [Pb]. The incorporated Pb is 80% removable after flushing with a Pb-free solution. At both surfaces the Pb coverage is similar, implying the surfaces have similar reactive site densities, however, the partitioning of the Pb is different for the two surfaces. These results suggest that even in cases where element coverage is similar at different surfaces of a mineral, the uptake mechanisms involved may be quite different, which can affect the long-term stability of the sorbed species at specific interfaces.<br/>

Lead sorption at the barite (001) and (210)-water Interfaces

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

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