Interfacial reactivity and NaOL adsorption mechanisms on magnesite and calcite: Insights from surface complexation model

A surface complexation model framework was developed to quantitatively describe carbonate mineral flotation mechanisms. • Magnesite and calcite both follow a three-zone dissolution mechanism jointly controlled by proton and surface complexation. • The intrinsic constants and site densities of protonation reactions on magnesite and calcite were quantitatively analyzed. • NaOL adsorption occurred via dissolved-ion-bridged bidentate-binuclear coordination on ≡MeOL and ≡CO 3 MeOL sites. For a long time, it has been quite difficult to effectively carry out flotation separation of magnesite and calcite owing to the fact that their physicochemical properties are essentially very similar. However, the primary interfacial mechanisms causing this similar flotation behavior are unknown, impeding predictions of site distribution in the carbonate mineral-collector system. In this study, a multiscale surface complexation modeling (SCM) combining dissolution kinetic, adsorption isotherm, and spectral characterization data was developed. The results demonstrate that magnesite and calcite followed a three-zone dissolution pattern, which was jointly controlled by proton and surface complexation reactions. The release of Mg 2+ and Ca 2+ ions from the crystal lattice regulated the evolution of surface sites and surface wettability. According to the SCM, the surface densities, protonation constants and species distributions of the magnesite and calcite were very similar. The control of sodium oleate (NaOL) adsorption was via dissolved-ion bridging bidentate-binuclear coordination mechanism operating on ≡MeOL and ≡CO 3 MeOL sites. Calcite demonstrated a marginally higher intrinsic binding affinity than that of magnesite, however, its offset by multisite interactions led to similar adsorption capacities and floatability. XPS and SEM-EDS evidence confirmed the formation of multisite complexes, which were also predicted by the SCM. These findings offer molecular insights into the differing adsorption behavior of NaOL, which enhances our understanding of the reactivity at the flotation interface of carbonate minerals. They could also provide a theoretical basis for controlling and predicting the flotation behavior of carbonate minerals.