Calcite plays a role as a sink for heavy metals in soils and sediments. Observation of the structural evolution of calcite surfaces during reaction in confined aqueous environments can provide an insight into the uptake mechanism. We explored temporal variations in the atomic structure of calcite (104) surfaces in contact with 1 mM CdCl2 solutions as a function of initial solution pH (pHi) using in situ high-resolution X-ray reflectivity. A limited solution volume (~ 1 mL per cm2 of the calcite surface area) was used to mimic pore environments where the interfacial reactivity was constrained by the availability of reactants. At pHi = 3, the calcite surface showed increased roughness, caused by dissolution, but limited sorption of Cd at the interface. At pHi = 4, most surfaces were covered with epitaxial otavite films that were 15–30 Å thick. These epitaxial films generally became thinner with increasing pHi. At pHi = 6, the growth was effectively limited to &lt;10 Å in thickness, which presumably resulted from slower dissolution of calcite at higher pHi combined with passivation of the calcite surface by the films. These results highlight the impact of dynamic variations in solution chemistry on the reactivity of calcite surfaces in confined aqueous media.

Effects of limited solution volume on the distribution of cadmium sorbed at the calcite (104)–water interface in acidic conditions

ACS Spring 2022

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