Ion adsorption processes are a likely initial step in the incorporation of divalent cations, such as Sr2+ and Pb2+, into barite. Here, we measured sorption on flat surfaces with relatively few defects and compared these results with surfaces that were reacted with various solutions to affect their surface roughness. The coverage and location of either lead (Pb) or strontium (Sr) sorbed to freshly cleaved (001) and (210) surfaces and reacted (001) surfaces were studied as a function of [Pb]aq or [Sr]aq using in situ specular x-ray reflectivity (XR) and resonant anomalous x-ray reflectivity (RAXR). At all surfaces, Sr and Pb incorporated into the topmost barite layer and adsorbed inner-sphere with a small outer-sphere fraction. We found the type of surface affects the extent of sorption, with roughly twice the amount of Sr or Pb sorbed to the (001) barite surface as compared with the (210) barite surface. Roughening of the (001) surface had little effect on Pb sorption at Robinson roughness parameters β &lt; 0.1, but roughly twice as much Pb2+ sorbed to samples at higher β. Similar analyses were made in the presence of Sr2+, but reacted samples had less sorption as compared with freshly cleaved samples. For both ions, there was little difference in the average position of the sorbed ions and the ratio of incorporated to adsorbed species for all samples. These results suggest that the (001) has a higher sorption capacity than the (210), but that capacity can be affected by roughening the surface.

Sr and Pb sorption to barite: The role of surface termination and roughness

ACS Spring 2022

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